Filed Pursuant to Rule 424(b)(5)
Registration No. 333-220267

The information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell the notes and are not soliciting an offer to buy the notes in any jurisdiction where the offer or sale is not permitted.

Subject to Completion

Preliminary Prospectus Supplement dated February 5, 2018

PROSPECTUS SUPPLEMENT

(To Prospectus Dated August 30, 2017)

MPLX LP

$             % Senior Notes due             

$             % Senior Notes due             

$             % Senior Notes due             

$             % Senior Notes due             

MPLX LP, or “MPLX,” “we” or “us,” is offering $        aggregate principal amount of     % Senior Notes due             , which we refer to as the “             notes,” $        aggregate principal amount of     % Senior Notes due             , which we refer to as the “             notes,” $        aggregate principal amount of     % Senior Notes due             , which we refer to as the “             notes” and $        aggregate principal amount of     % Senior Notes due             , which we refer to as the “             notes.” We collectively refer to the              notes, the              notes, the              notes and the              notes as the “notes.”

We will pay interest on each series of the notes semi-annually in arrears on                  and                 of each year they are outstanding, commencing on                     , 2018.

We have the option to redeem some or all of the notes of any series at any time and from time to time, as described under the heading “Description of the Notes—Optional Redemption.”

The notes will be unsecured unsubordinated obligations of MPLX and will rank equally with all of MPLX’s other unsecured unsubordinated debt from time to time outstanding, but will be effectively junior to MPLX’s secured indebtedness to the extent of the value of the relevant collateral. The notes will not be the obligation of any of MPLX’s subsidiaries and will be structurally subordinated to all indebtedness and other obligations of MPLX’s subsidiaries.

Each series of notes is a new issue of securities with no established trading market. We do not intend to apply to list the notes on any securities exchange or to have the notes quoted on any automated quotation system.

Investing in the notes involves risks. You should carefully consider the risk factors on page S-11 of this prospectus supplement and in the accompanying prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Delivery of the notes offered hereby in book-entry form will be made only through the facilities of The Depository Trust Company for the accounts of its participants, including Euroclear Bank, S.A./N.V. and Clearstream Banking, société anonyme, on or about February     , 2018. This settlement date may affect trading of the notes. See “Underwriting (Conflicts of Interest).”

Joint Global Coordinators and Book-Running Managers

Joint Book-Running Managers

The date of this prospectus supplement is February     , 2018.

TABLE OF CONTENTS

PROSPECTUS SUPPLEMENT

ABOUT THIS PROSPECTUS SUPPLEMENT

We provide information to you about this offering in two parts. The first part is this prospectus supplement which describes the specific terms of this offering and adds to, updates and changes information contained in the accompanying prospectus. The second part is the accompanying prospectus, which provides general information, some of which may not apply to this offering. This prospectus supplement should be read in conjunction with the accompanying prospectus. To the extent the information contained in this prospectus supplement is inconsistent with the information in the accompanying prospectus, you should rely on the information in this prospectus supplement.

You should rely only on the information contained or incorporated by reference in this prospectus supplement, in the accompanying prospectus, or in any free writing prospectus that we may provide to you. We have not, and the underwriters have not, authorized anyone to provide you with different information. We are not, and the underwriters are not, making offers to sell the notes in any jurisdiction in which an offer or solicitation is not authorized or in which the person making such offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make an offer or solicitation. You should not assume that the information contained in this prospectus supplement, the accompanying prospectus, or any document incorporated by reference is accurate as of any date other than the date on the cover page of those respective documents. Our business, financial condition, results of operations and prospects may have changed since those respective dates.

Except as otherwise indicated, references in this prospectus supplement to “MPLX,” the “Partnership,” “we,” “us” and “our” refer to MPLX LP and its consolidated subsidiaries. References to “MPLX LP” refer to MPLX LP but not its subsidiaries. References to “MarkWest” refer to our wholly-owned subsidiary MarkWest Energy Partners, L.P. and its subsidiaries. References to “MPC” refer to Marathon Petroleum Corporation and its consolidated subsidiaries, excluding MPLX LP and its consolidated subsidiaries.

WHERE YOU CAN FIND MORE INFORMATION

We are subject to the informational reporting requirements of the Securities Exchange Act of 1934, or the Exchange Act. We file annual, quarterly and current reports and other information with the Securities and Exchange Commission, or the SEC. You can read and copy these materials at the SEC’s public reference room at 100 F Street, N.E., Washington, D.C. 20549. You can obtain information about the operation of the SEC’s public reference room by calling the SEC at 1-800-SEC-0330. The SEC also maintains an Internet site that contains information MPLX has filed electronically with the SEC, which you can access over the Internet at http://www.sec.gov. You can also obtain information about MPLX at our website at http://www.mplx.com. We do not intend for information contained on, or accessible through, our website to be part of this prospectus supplement or the accompanying prospectus, other than documents that we file with the SEC that are incorporated by reference in this prospectus supplement or the accompanying prospectus.

INFORMATION WE INCORPORATE BY REFERENCE

The SEC allows us to “incorporate by reference” into this prospectus supplement and the accompanying prospectus the information in documents we have filed with the SEC. This means that we can disclose important information to you without actually including the specific information in the prospectus supplement or accompanying prospectus by referring you to other documents filed separately with the SEC. These other documents contain important information about us, our financial condition and results of operation. The information we incorporate by reference is considered to be a part of this prospectus supplement and the accompanying prospectus. Information that we file with the SEC after the date of this prospectus supplement will automatically update and supersede the information contained in this prospectus supplement and the accompanying prospectus. Any statement contained in any document incorporated or deemed to be incorporated

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by reference herein shall be deemed to be modified or superseded for purposes of this prospectus supplement and the accompanying prospectus to the extent that a statement contained in or omitted from this prospectus supplement or the accompanying prospectus, or in any other subsequently filed document that also is or is deemed to be incorporated by reference herein, modifies or supersedes such statement. Any such statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus supplement and the accompanying prospectus.

We incorporate by reference the following documents into this prospectus supplement:

We also incorporate by reference any future filings we make with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Exchange Act (excluding information deemed to be furnished and not filed with the SEC) until the termination of this offering. We do not and will not, however, incorporate by reference in this prospectus supplement any documents or portions thereof that are not deemed “filed” with the SEC, including any information furnished pursuant to Item 2.02 or Item 7.01 of our Current Reports on Form 8-K unless, and except to the extent, specified in such current reports.

You may request a copy of these filings, other than an exhibit to these filings unless we have specifically incorporated that exhibit by reference into the filing, at no cost, by writing or telephoning MPLX at the following address or telephone number:

MPLX LP

200 E. Hardin Street

Findlay, Ohio 45840

Attention: Investor Relations

Telephone: (419) 421-2414

DISCLOSURES REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement and the accompanying prospectus, including the documents incorporated herein by reference, includes forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, or the Securities Act, and Section 21E of the Exchange Act. You can identify our forward-looking statements by words such as “anticipate,” “believe,” “design,” “estimate,” “objective,” “expect,” “forecast,” “goal,” “guidance,” “imply,” “intend,” “opportunity,” “outlook,” “plan,” “position,” “potential,” “predict,” “project,” “prospective,” “pursue,” “seek,” “strategy,” “target,” “could,” “may,” “should,” “would,” “will” or other similar expressions that convey the uncertainty of future events or outcomes. When considering these

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forward-looking statements, you should keep in mind the risk factors and other cautionary statements contained in this prospectus supplement and the documents we have incorporated by reference.

Forward-looking statements include, but are not limited to, statements that relate to, or statements that are subject to risks, contingencies or uncertainties that relate to:

We have based our forward-looking statements on our current expectations, estimates and projections about our industry and our partnership. We caution that these statements are not guarantees of future performance, and you should not rely unduly on them, as they involve risks, uncertainties, and assumptions that we cannot predict. In addition, we have based many of these forward-looking statements on assumptions about future events that may prove to be inaccurate.

While our management considers these assumptions to be reasonable, they are inherently subject to significant business, economic, competitive, regulatory and other risks, contingencies and uncertainties, most of which are difficult to predict and many of which are beyond our control. Accordingly, our actual results may differ materially from the future performance that we have expressed or forecast in our forward-looking statements. Differences between actual results and any future performance suggested in our forward-looking statements could result from a variety of factors, including the following:

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We do not undertake any obligation to update the forward-looking statements included or incorporated by reference in this prospectus supplement or the accompanying prospectus, unless we are required by applicable securities laws to do so.

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RISK FACTORS

An investment in the notes involves risk. Prior to making a decision about investing in the notes, and in consultation with your financial and legal advisors, you should carefully consider the following risk factors regarding the notes and this offering, as well as the risk factors incorporated by reference in this prospectus supplement from our Annual Report on Form 10-K for the year ended December 31, 2016 under the heading “Risk Factors,” as amended or supplemented by subsequent Quarterly Reports on Form 10-Q that are incorporated by reference in this prospectus supplement and other filings we may make from time to time with the SEC. You should also refer to the other information in this prospectus supplement and the accompanying prospectus, including our financial statements and the related notes incorporated by reference into this prospectus supplement and the accompanying prospectus. Additional risks and uncertainties that are not yet identified may also materially harm our business, operating results and financial condition and could result in a complete loss of your investment.

Risks Relating to this Offering and the Notes

Our existing and future debt may limit cash flow available to invest in the ongoing needs of our business and could prevent us from fulfilling our obligations under our outstanding debt, including the notes.

We have substantial existing debt. As of September 30, 2017, we had total debt of approximately $7.5 billion. We also have the capacity under our revolving credit agreements and the indenture to incur substantial additional debt. Our level of debt could have important consequences. For example, it could:

Additionally, any failure to meet required payments on our debt, or failure to comply with any covenants in the instruments governing our debt, could result in an event of default under the terms of those instruments. In the event of such default, the holders of such debt could elect to declare all the amounts outstanding under such instruments to be due and payable.

Changes in our credit ratings may adversely affect the value of the notes.

The ratings assigned to the notes could be lowered, suspended or withdrawn entirely by the rating agencies if, in each rating agency’s judgment, circumstances warrant. Actual or anticipated changes or downgrades in our credit ratings, including any announcement that our ratings are under review for a downgrade, could affect the market value of the notes.

The indenture does not restrict the amount of additional debt that we and our subsidiaries may incur and our revolving credit agreements permit us and our subsidiaries to incur substantial additional unsecured debt.

The notes and the indenture will not place any limitation on the amount of unsecured debt that we may incur and our revolving credit agreements permit us and our subsidiaries to incur substantial additional unsecured debt. Our incurrence of additional debt, and the incurrence of additional debt by any of our subsidiaries, may have important consequences for you as a holder of the notes, including making it more difficult for us to satisfy our obligations with respect to the notes, a loss in the market value of the notes and a risk that the credit rating of the notes is downgraded or withdrawn.

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The terms of the notes do not require us to offer to repurchase the notes upon a “change of control” transaction.

The terms of the notes do not require us to offer to repurchase the notes upon a “change of control” transaction. Accordingly, holders will not have the right to require us to repurchase the notes if we enter into transactions that result in a change of control of our partnership. Certain of our existing senior notes and other existing debt obligations provide such rights to holders of those obligations.

MPLX LP is a holding company and depends on dividends and other distributions from our subsidiaries.

MPLX LP is a holding company with limited direct operations. Its principal assets are the equity interests that it holds in its subsidiaries, including MarkWest. As a result, it depends on dividends and other distributions from its subsidiaries to generate the funds necessary to meet its financial obligations, including the payment of principal and interest on its outstanding indebtedness. MPLX LP’s subsidiaries are legally distinct from MPLX LP and generally have no obligation to pay amounts due on MPLX LP’s indebtedness or to make funds available to MPLX LP for such payment. In addition, certain of MPLX LP’s subsidiaries have existing debt obligations and are permitted under the terms of the indenture governing the notes to incur additional indebtedness or enter into other agreements that may restrict or prohibit the making of distributions, the payment of dividends or the making of loans by such subsidiaries to MPLX LP. MPLX LP cannot assure you that the agreements governing the current and future indebtedness or other activities of its subsidiaries will permit its subsidiaries to provide MPLX LP with sufficient dividends, distributions or loans to fund payments on the notes when due.

None of our properties have been determined to be a principal property under the indenture.

The indenture governing the notes includes covenants that, among other things, limit our ability to create or permit to exist mortgages and other liens and enter into sale and leaseback transactions with respect to principal properties. However, our Board of Directors has the discretion to determine whether any property is a principal property and, as of the date of this prospectus supplement, our Board of Directors has not determined that any of our properties is a principal property under the indenture.

An increase in market interest rates could result in a decrease in the value of the notes.

In general, as market interest rates rise, notes bearing interest at a fixed rate decline in value because the premium, if any, over market interest rates will decline. Consequently, if you purchase any of the notes and market interest rates increase, the market values of such notes may decline. We cannot predict the future level of market interest rates.

Active trading markets for the notes may not develop.

Each series of the notes is a new issue of securities with no established trading market. We do not intend to apply for listing of the notes on any securities exchange or any automated quotation system. Accordingly, there can be no assurance that a trading market for the notes will ever develop or will be maintained. If a trading market does not develop or is not maintained, you may find it difficult or impossible to resell the notes. Further, there can be no assurance as to the liquidity of any market that may develop for such notes, your ability to sell such notes or the price at which you will be able to sell such notes. Future trading prices of the notes will depend on many factors, including prevailing interest rates, our financial condition and results of operations, the then-current ratings assigned to the notes and the markets for similar securities.

Any trading market that develops would be affected by many factors independent of and in addition to the foregoing, including:

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The underwriters have advised us that they currently intend to make a market in each series of the notes, but they are not obligated to do so and may cease market-making at any time without notice.

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RATIO OF EARNINGS TO FIXED CHARGES

Our ratios of earnings to fixed charges for each of the periods indicated are as follows:

The term “earnings” is the amount resulting from adding the following items to the extent applicable:

and subtracting from the total the following:

For this purpose, “fixed charges” consists of:

Preference security distributions is the amount of pre-tax earnings that was required to pay distributions on our outstanding Series A Preferred units. On May 13, 2016, we issued 30,769,232 Series A Preferred units, all of which were outstanding as of September 30, 2017.

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USE OF PROCEEDS

We expect to receive net proceeds, after deducting underwriting discounts and estimated offering expenses payable by us, of approximately $        from this offering.

We intend to use the net proceeds from this offering to repay the principal amount and accrued interest on the $4.1 billion term loan borrowing made pursuant to the term loan agreement and to pay related fees and expenses. We will use the remaining net proceeds of this offering, if any, to repay borrowings under our revolving credit facility and the MPC intercompany loan agreement and/or for general partnership purposes, which may include, from time to time, acquisitions, capital expenditures and the payment of distributions. Pending final use, we may invest the net proceeds from this offering in short-term marketable securities.

As of February 1, 2018, $4.1 billion of indebtedness was outstanding under the term loan agreement. We used the proceeds of the term loan borrowing to fund the cash portion of the consideration payable by us in the acquisition of Refining Logistics and Fuels Distribution. The term loan borrowing matures on December 31, 2018. As of February 1, 2018, the term loan borrowing bore interest at a rate of 2.85% per annum.

As of February 1, 2018, approximately $508 million of indebtedness was outstanding under our revolving credit facility. We used borrowings under our revolving credit facility for general partnership purposes. The revolving credit facility matures on July 21, 2022. As of February 1, 2018, outstanding borrowings under the revolving credit agreement bore interest at a weighted average rate of 2.96% per annum.

As of February 1, 2018, approximately $431 million of indebtedness was outstanding under the MPC intercompany loan. We used borrowings under the MPC intercompany loan for general partnership purposes. The MPC intercompany loan matures on December 4, 2020. As of February 1, 2018, outstanding borrowings under the MPC intercompany loan agreement bore interest at a rate of 3.08% per annum.

Affiliates of certain of the underwriters are lenders under our credit facilities and, accordingly, will receive a portion of the net proceeds of this offering. Accordingly, this offering is being made in compliance with FINRA Rule 5121. See “Underwriting (Conflicts of Interest).”

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CAPITALIZATION

The following table sets forth our capitalization as of September 30, 2017 (1) on a historical basis; (2) on an adjusted basis to give effect to the acquisition of Refining Logistics and Fuels Distribution, the $4.1 billion borrowing under the term loan agreement and the GP/IDR Restructuring; and (3) on an adjusted basis to give effect to this offering and the use of proceeds as described herein.

You should read this table in conjunction with our consolidated financial statements, the related notes and other financial information contained in our Annual Report on Form 10-K for the fiscal year ended December 31, 2016, and our Quarterly Report on Form 10-Q for the quarter ended September 30, 2017, which are incorporated by reference into this prospectus supplement and the accompanying prospectus.

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DESCRIPTION OF OTHER INDEBTEDNESS

Revolving Credit Facility

MPLX LP entered into a revolving credit agreement, dated as of July 21, 2017, providing for a $2.25 billion unsecured revolving credit facility, which we refer to as the “revolving credit facility.” The revolving credit facility expires on July 21, 2022 but may be extended up to two additional one-year periods subject to the consent of the lenders holding a majority of the commitments, provided that the commitments held by any non-consenting lenders will terminate on the then effective maturity date. The revolving credit facility includes letter of credit issuing capacity of up to $222 million and swingline loan capacity of up to $100 million. The revolving credit facility may be increased by up to an additional $500 million, subject to certain customary conditions, including the consent of the lenders whose commitments would increase.

We pay interest on outstanding borrowings under the revolving credit facility based upon either the adjusted LIBO rate or an alternate base rate, at our election, plus, in each case, a specified margin. In addition, we pay various fees and expenses in connection with the revolving credit facility, including administrative agent fees, commitment fees on the unused portion of the revolving credit facility and fees with respect to issued and outstanding letters of credit. The margins above the applicable benchmark interest rates and commitment fees fluctuate based on the credit ratings in effect from time to time on our long-term debt.

The revolving credit agreement contains certain representations and warranties, affirmative and restrictive covenants and events of default that we consider to be usual and customary for an agreement of this type, including a financial covenant that requires us to maintain a ratio of consolidated total debt as of the end of each fiscal quarter to consolidated EBITDA for the prior four fiscal quarters of no greater than 5.0 to 1.0 (or 5.5 to 1.0 for up to two fiscal quarters following certain acquisitions). Consolidated EBITDA is subject to adjustments for certain acquisitions and dispositions completed and capital projects undertaken during the relevant period. Other covenants, among other things, restrict our ability to incur debt, create liens on our assets and enter into transactions with affiliates.

As of September 30, 2017, there were $420 million of borrowings and $3 million of letters of credit outstanding under the revolving credit facility.

Term Loan Facility

MPLX LP entered into a term loan agreement, dated as of January 2, 2018, to fund the cash portion of the consideration payable by us in the acquisition of Refining Logistics and Fuels Distribution and related transaction expenses. The term loan agreement provides for a $4.1 billion unsecured term loan facility, which we refer to as the “term loan facility.” The term loan facility was funded in full concurrently with the closing of the acquisition. The $4.1 billion term loan matures on December 31, 2018, subject to mandatory prepayment provisions in the event that we receive cash proceeds from certain debt or equity offerings or issuances or certain asset dispositions prior to the maturity date, in each case, subject to certain exceptions set forth in the term loan agreement.

We pay interest on the outstanding term loan borrowing based upon either the adjusted LIBO rate or an alternate base rate, at our election, plus, in each case, a specified margin. In addition, we paid customary upfront fees, an administrative agent fee and various expenses in connection with establishing and funding of the term loan facility. We are also obligated to pay duration fees if the term loan remains outstanding for 90, 180 and 270 days following February 1, 2018. The margins above the applicable benchmark interest rates fluctuate based on the credit ratings in effect from time to time on our long-term debt and the amount of time the term loan remains outstanding.

The term loan agreement contains certain representations and warranties, affirmative and restrictive covenants and events of default that we consider to be usual and customary for an agreement of this type and that are substantially similar to those contained in the revolving credit agreement.

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We intend to repay the outstanding principal amount of the term loan, together with accrued and unpaid interest, with the proceeds of this offering.

MPC Intercompany Loan Agreement

On December 4, 2015, MPLX LP entered into a loan agreement with MPC Investment LLC, a wholly-owned subsidiary of MPC, which we refer to as “MPC Investment.” Under the terms of the loan agreement, which we refer to as the “MPC intercompany loan agreement,” MPC Investment will make a loan or loans to MPLX LP on a revolving basis as requested by MPLX LP and as agreed to by MPC Investment in an amount or amounts that do not result in the aggregate principal amount of all loans outstanding exceeding $500 million at any one time, which amount may from time-to-time be increased or decreased as mutually agreed to by us and MPC Investment. The entire unpaid principal amount of any loans, together with all accrued and unpaid interest and other amounts (if any), is due and payable on December 4, 2020, provided that MPC Investment may demand payment of all or any portion of the outstanding principal amount of any loans, together with all accrued and unpaid interest and other amounts (if any), at any time prior thereto. Borrowings under the MPC intercompany loan agreement bear interest at LIBOR plus 1.50%. As of September 30, 2017, there were $202 million borrowings outstanding under the MPC intercompany loan agreement.

MPLX LP Senior Notes

On February 12, 2015, MPLX LP issued $500 million in aggregate principal amount of 4.000% senior notes due 2025. The 4.000% 2025 senior notes mature on February 15, 2025. Interest on the 4.000% senior notes due 2025 is payable on February 15^th and August 15^th of each year prior to maturity.

In connection with the MarkWest Merger, we assumed MarkWest’s outstanding debt, which included $4.1 billion aggregate principal amount of senior notes. On December 22, 2015, approximately $4.04 billion in aggregate principal amount of MarkWest’s outstanding senior notes were exchanged for an aggregate principal amount of approximately $4.04 billion of new unsecured senior notes issued by MPLX LP in an exchange offer and consent solicitation undertaken by MPLX LP and MarkWest.

The MPLX LP senior notes issued in the exchange offer and consent solicitation consist of approximately $710 million aggregate principal amount of 5.500% senior notes due February 15, 2023, approximately $989 million aggregate principal amount of 4.500% senior notes due July 15, 2023, approximately $1.15 billion aggregate principal amount of 4.875% senior notes due December 1, 2024 and approximately $1.19 billion aggregate principal amount of 4.875% senior notes due June 1, 2025. Interest on such MPLX LP senior notes is payable semi-annually in arrears on the following dates of each year prior to their maturity: February 15th and August 15^th with respect to the 5.500% senior notes due 2023; January 15th and July 15th with respect to the 4.500% senior notes due 2023; and June 1st and December 1st with respect to the 4.875% senior notes due 2024 and the 4.875% senior notes due 2025.

On February 10, 2017, MPLX LP issued $1.25 billion in aggregate principal amount of 4.125% senior notes due March 1, 2027 and $1.0 billion in aggregate principal amount of 5.200% senior notes due March 1, 2047. Interest on the 4.125% senior notes due 2027 and the 5.200% senior notes due 2047 is payable semi-annually in arrears on March 1^st and September 1^st of each year prior to maturity.

Each series of the MPLX LP senior notes was issued under the same indenture that will govern the notes offered hereby. The MPLX LP senior notes are the direct, unsecured unsubordinated obligations of MPLX LP and rank equally with all other senior unsecured debt of MPLX LP, including, when issued, the notes offered hereby. The MPLX LP senior notes are effectively junior to our secured indebtedness to the extent of the value of the relevant collateral and effectively subordinated to all indebtedness and other obligations of our subsidiaries.

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MarkWest Senior Notes

After giving effect to the exchange offer and consent solicitation described above, as of September 30, 2016, MarkWest had outstanding approximately $40 million aggregate principal amount of 5.500% senior notes due February 15, 2023, approximately $11 million aggregate principal amount of 4.500% senior notes due July 15, 2023, approximately $1 million aggregate principal amount of 4.875% senior notes due December 1, 2024 and approximately $11 million aggregate principal amount of 4.875% senior notes due June 1, 2025. Interest on the MarkWest senior notes is payable semi-annually in arrears on the following dates of each year prior to their maturity: February 15th and August 15th with respect to the 5.500% 2023 senior notes; January 15th and July 15th with respect to the 4.500% 2023 senior notes; and June 1st and December 1st with respect to the 4.875% 2024 senior notes and the 4.875% 2025 senior notes.

The outstanding MarkWest senior notes are unsecured unsubordinated indebtedness of MarkWest, and as such, are structurally senior to all of MPLX’s unsecured unsubordinated debt, including the MPLX senior notes currently outstanding and the notes offered hereby.

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DESCRIPTION OF THE NOTES

The notes will be issued under an indenture, dated as of February 12, 2015, as supplemented, between MPLX LP, as issuer, and The Bank of New York Mellon Trust Company, N.A., as the trustee (the “trustee”), as further supplemented by the eighth supplemental indenture, ninth supplemental indenture, tenth supplemental indenture, eleventh supplemental indenture and twelfth supplemental indenture, each to be entered into between MPLX LP and the trustee (the “indenture”). The following description is a summary of the material terms of the indenture and the notes and is intended to supplement, and to the extent inconsistent, to replace, the more general terms and provisions of the debt securities described in the accompanying prospectus, to which we refer you. You should read the indenture and the notes for more details regarding our obligations and your rights with respect to the notes. In this description of the notes references to “MPLX LP,” the “Company,” “we” or “us” refer only to MPLX LP and not to any of its subsidiaries.

General

We are offering $        total aggregate principal amount of notes, consisting of $        aggregate principal amount of the              notes, $        aggregate principal amount of the              notes, $        aggregate principal amount of the              notes and $        aggregate principal amount of the              notes. The              notes will mature on                 ,              and bear interest at the rate of     % per annum. The              notes will mature on                 ,              and bear interest at the rate of     % per annum. The              notes will mature on                 ,              and bear interest at the rate of     % per annum. The              notes will mature on                 ,              and bear interest at the rate of     % per annum.

Interest on each series of the notes will be payable semi-annually on                  and                 of each year, beginning on                 , 2018, to the persons in whose names the notes are registered at the close of business on                  and                 , respectively, preceding the interest payment date. Interest on each series of the notes will be paid on the basis of a 360-day year consisting of twelve 30-day months.

If any interest payment date, stated maturity date or redemption date falls on a day that is not a business day, the payment will be made on the next business day and no interest will accrue for the period from and after such interest payment date, stated maturity date or redemption date.

Each series of the notes will be issued in fully registered form only in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

We may, without the consent of the holders, increase the principal amount of each series of the notes in the future, on the same terms and conditions, other than the public offering price, original interest accrual date and initial interest payment date, and with the same CUSIP number as the applicable series of notes being offered by this prospectus supplement. We will not issue any such additional notes of a series unless the additional notes are fungible with the applicable series of the notes being offered hereby for U.S. federal income tax purposes. The applicable series of the notes and any such additional notes subsequently issued under the indenture will be treated as a single series or class for all purposes under the indenture, including, without limitation, waivers, amendments and redemptions.

The indenture does not limit the amount of debt that we may issue under the indenture, nor the amount of other unsecured debt or securities that we or any of our subsidiaries may issue. We may issue debt securities under the indenture from time to time in one or more series, each in an amount authorized prior to issuance.

Other than the restrictions contained in the indenture on liens and sale/leaseback transactions described below under “—Certain Covenants,” the indenture does not contain any covenants or other provisions designed to protect holders of the debt securities in the event we participate in a “change of control” or highly leveraged transaction. In addition, the indenture does not limit our ability to guarantee any indebtedness of our subsidiaries or any other person.

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Optional Redemption

Except as otherwise described below, each series of the notes will be redeemable in whole at any time or in part from time to time, at our option, prior to the applicable Par Call Date (defined below), at a redemption price equal to the greater of:

We will also pay accrued and unpaid interest on the principal amount being redeemed to, but not including, the date of redemption.

If any series of the notes are redeemed on or after the applicable Par Call Date, we will pay a redemption price equal to 100% of the principal amount of the notes redeemed. We will also pay accrued and unpaid interest on the principal amount being redeemed to, but not including, the date of redemption.

For purposes of the foregoing discussion of optional redemption, the following definitions are applicable:

“Business Day” means any Monday, Tuesday, Wednesday, Thursday or Friday that is not a day on which banking institutions in New York, New York or any “Place of Payment,” which the indenture defines to mean the place or places, if any, in addition to or instead of the Corporate Trustee Office of the trustee, where the principal of, and premium, if any, and interest on debt securities of the series will be payable, are authorized or obligated by law, regulation or executive order to close.

“Comparable Treasury Issue” means the United States Treasury security selected by an Independent Investment Banker as having a maturity comparable to the remaining term (assuming, for this purpose, the notes matured on the applicable Par Call Date), which we refer to as the “Remaining Life,” of the notes to be redeemed that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of such notes.

“Comparable Treasury Price” means, with respect to any redemption date, (1) the average, as determined by us, of the Reference Treasury Dealer Quotations for such redemption date, after excluding the highest and lowest Reference Treasury Dealer Quotations, or (2) if we obtain fewer than six such Reference Treasury Dealer Quotations, the average of all such quotations.

“Independent Investment Banker” means one of the Reference Treasury Dealers that we appoint to act as the Independent Investment Banker from time to time.

“Par Call Date” means                in the case of the              notes,                in the case of the              notes,                in the case of the              notes and                 in the case of the              notes.

“Reference Treasury Dealer” means each of Merrill Lynch, Pierce, Fenner & Smith Incorporated, Barclays Capital Inc., Mizuho Securities USA LLC, J.P. Morgan Securities LLC and Wells Fargo Securities, LLC, and one additional dealer in U.S. Government securities selected by us, each of which we refer to as a “Primary Treasury Dealer,” and their respective successors that we specify from time to time; provided, however, that if any of them ceases to be a Primary Treasury Dealer, we will substitute therefor another Primary Treasury Dealer.

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“Reference Treasury Dealer Quotations” means, with respect to each Reference Treasury Dealer and any redemption date, the average, as determined by us, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to us by such Reference Treasury Dealer at 5:00 p.m., New York City time, on the third Business Day preceding such redemption date.

“Treasury Rate” means, with respect to any redemption date, the rate per year equal to: (1) the yield, under the heading which represents the average for the immediately preceding week, appearing in the most recently published statistical release designated “H.15” or any successor publication which is published weekly by the Board of Governors of the Federal Reserve System and which establishes yields on actively traded United States Treasury securities adjusted to constant maturity under the caption “Treasury Constant Maturities,” for the maturity corresponding to the Comparable Treasury Issue; provided that, if no maturity is within three months before or after the Remaining Life of the notes to be redeemed, yields for the two published maturities most closely corresponding to the Comparable Treasury Issue shall be determined and the Treasury Rate shall be interpolated or extrapolated from those yields on a straight-line basis, rounding to the nearest month; or (2) if such release (or any successor release) is not published during the week preceding the calculation date or does not contain such yields, the rate per year equal to the semiannual equivalent yield to maturity of the Comparable Treasury Issue, calculated using a price for the Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the Comparable Treasury Price for such redemption date. The Treasury Rate shall be calculated on the third Business Day preceding the redemption date.

Notice of redemption will be given at least 30 but not more than 60 days before the redemption date to each holder of record of each series of the notes to be redeemed at its registered address. However, such notice may be given more than 60 days before the redemption date if the notice is given in connection with a satisfaction and discharge. The notice of redemption for each series of the notes will state, among other things, the amount of the notes to be redeemed, the redemption date, the redemption price and the place or places that payment will be made upon presentation and surrender of the notes to be redeemed. Unless we default in the payment of the redemption price, interest will cease to accrue on any notes that have been called for redemption at the redemption date. If fewer than all of the notes of a series are to be redeemed at any time, the trustee will select the particular notes of the applicable series or portions thereof for redemption from the outstanding notes of the applicable series not previously called on a pro rata basis, by lot or by such method as the trustee deems fair and appropriate (or, in the case of notes represented by a global security, by such method as The Depository Trust Corporation, the “DTC,” may require).

Open Market Purchases

MPLX LP or any of its affiliates may at any time and from time to time purchase notes in the open market or otherwise.

Sinking Fund

There is no provision for a sinking fund for the notes.

Ranking

The notes will be unsecured and unsubordinated obligations of MPLX LP and will rank equally with all other existing and future unsecured and unsubordinated indebtedness of MPLX LP, but will be effectively junior to MPLX LP’s secured indebtedness to the extent of the value of the relevant collateral. The notes will not be the obligations of any of the issuer’s subsidiaries and will be effectively subordinated to all indebtedness and other obligations of such subsidiaries.

MPLX LP is a holding company and derives substantially all of its operating income from, and holds substantially all of its assets through, its subsidiaries. As a result, it depends on distributions of cash flow and

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earnings from its subsidiaries in order to meet its payment obligations under the notes and its other debt obligations. These subsidiaries are separate and distinct legal entities and will have no obligation to pay any amounts due on such debt securities, including the notes, or to provide MPLX LP with funds for its payment obligations, whether by dividends, distributions, loans or otherwise. As a result, the notes will be structurally subordinated to the liabilities of the issuer’s subsidiaries, including trade payables. In addition, provisions of applicable law, such as those limiting the legal sources of dividends, could limit the ability of such subsidiaries to make payments or other distributions to MPLX LP and such subsidiaries could agree to contractual restrictions on their ability to make distributions. As of September 30, 2017, MPLX LP’s consolidated subsidiaries had approximately $70 million of indebtedness. MPLX LP’s consolidated indebtedness, as of September 30, 2017, was approximately $7.5 billion. On an as adjusted basis, giving effect to the issuance of the notes in this offering and the use of proceeds as described under the heading “Use of Proceeds,” MPLX LP’s consolidated indebtedness, as of September 30, 2017, would have been $        million. See “Use of Proceeds” and “Capitalization.”

Certain Covenants

Creation of Certain Liens

If MPLX LP, or any subsidiary of MPLX LP, mortgages or encumbers as security for money borrowed any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (1) is located in the United States and (2) is determined to be a principal property by the Board of Directors in its discretion, MPLX LP will, or will cause such subsidiary to, secure the notes and all other debt securities issued under the indenture equally and ratably with all obligations secured by the mortgage then being given. This covenant will not apply in the case of any mortgage:

In addition, MPLX LP may, and may permit its subsidiaries to, grant mortgages or incur liens on property covered by the restriction described above as long as the net book value of the property so encumbered, together with all property subject to the restriction on sale and leaseback transactions described below, does not, at the time such mortgage or lien is granted, exceed 15% of MPLX LP’s “Consolidated Net Tangible Assets,” which the indenture defines to mean the aggregate value of all assets of MPLX LP and its subsidiaries after deducting:

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all determined in conformity with generally accepted accounting principles and calculated on a basis consistent with our most recent audited consolidated financial statements.

The indenture defines “Board of Directors” as the Board of Directors of the issuer’s general partner or any authorized committee thereof or any directors and/or officers of the issuer’s general partner to whom such Board of Directors or such committee shall have duly delegated its authority to act under the indenture. If the issuer shall change its form of entity to other than a limited partnership, the references to the Board of Directors shall mean the Board of Directors (or other comparable governing body) of the issuer.

Limitations on Certain Sale and Leaseback Transactions

MPLX LP and its subsidiaries are generally prohibited from selling and leasing back the principal properties described above under “—Creation of Certain Liens.” However, this covenant will not apply if:

As of the date of this prospectus supplement, neither MPLX LP nor any subsidiary of MPLX LP has any property that the Board of Directors has determined to be a principal property under the indenture.

Merger, Consolidation and Sale of Assets

The indenture provides that MPLX LP may not consolidate or amalgamate with or merge with or into any other person, or sell, convey, transfer, lease or otherwise dispose of all or substantially all its assets to any person, whether in a single transaction or a series of related transactions unless:

In the case of any consolidation, amalgamation or merger in which MPLX LP is not the continuing entity, or disposition of all or substantially all of the assets of MPLX LP, the successor will succeed to and be substituted

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for MPLX LP with the same effect as if it had been an original party to the indenture, and, except in the case of a lease of all or substantially all of MPLX LP’s assets, the predecessor entity will be relieved of any further obligation under the indenture and the notes.

Events of Default

The indenture defines an event of default with respect to each series of the notes as being:

MPLX LP is required annually to deliver to the trustee a certificate stating that a review of the activities of MPLX LP and its subsidiaries has been made and to the best of each signer’s knowledge, MPLX LP has performed and fulfilled every covenant contained in the indenture and is not in default in the performance or observance of any of the terms, provisions and conditions of the indenture.

In case an event of default (other than an event of default involving an event of bankruptcy, insolvency or reorganization of MPLX LP) shall occur and be continuing with respect to a series of the notes, the trustee or the holders of not less than 25% in aggregate principal amount of such series of the notes then outstanding may declare the principal of, premium, if any, and interest on such series of the notes to be due and payable immediately. If an event of default relating to any event of bankruptcy, insolvency or reorganization of MPLX LP occurs, the principal of, premium, if any, and interest on all the notes then outstanding of such series will become immediately due and payable without any declaration or other act on the part of the trustee or any holder. The holders of a majority in aggregate principal amount of such series of the notes may in some cases rescind this accelerated payment requirement. Depending on the terms of our other indebtedness, an event of default may give rise to cross defaults on our other indebtedness.

Holders of not less than a majority in aggregate principal amount of each series of the notes then outstanding may waive any past default or event of default except a default or event of default:

Any default that is so waived will cease to exist and any event of default arising from that default will be deemed to be cured for every purpose under the indenture, but no such waiver will extend to any subsequent or other default or impair any right arising from a subsequent or other default.

No holder of any series of the notes may institute any action or proceeding under the indenture or for the appointment of a receiver or a trustee, or for any other remedy unless:

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Holders of notes, however, are entitled at any time to bring a lawsuit for the payment of principal of, and premium, if any, and interest on their notes on or after its due date. It is intended that rights provided for holders of the notes under the indenture are for the equal and ratable benefit of all holders of the notes.

Modification and Waiver

MPLX LP and the trustee may modify the indenture or any supplemental indenture without the consent of any holders of the notes with respect to specific matters, including:

MPLX LP and the trustee may otherwise modify the indenture with the written consent of the holders of not less than a majority in aggregate principal amount of each series of the notes affected. However, without the consent of the holder of each outstanding note affected, no modification may:

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Except in limited circumstances, MPLX LP may set any day as a record date for the purpose of determining the holders of outstanding notes of each series entitled to give or take any direction, notice, consent, waiver or other action under the indenture. In limited circumstances, the trustee may set a record date. To be effective, the action must be taken by holders of the requisite principal amount of such notes computed as of the record date.

Defeasance

The indenture provides that, upon satisfaction of the requirements described below, we may terminate all of our obligations under each series of the notes and the indenture, known as legal defeasance, other than our obligation:

In addition, we may terminate our obligation to comply with certain restrictive covenants under each series of the notes or the indenture, including the restrictions contained in the indenture on liens and sale/leaseback transactions described above under “—Certain Covenants,” known as covenant defeasance.

We may exercise our legal defeasance option even if we have previously exercised our covenant defeasance option. If we exercise our legal defeasance option, payment of each series of the notes may not be accelerated because of the occurrence of any events of default. If we exercise our covenant defeasance option, payment of each series of the notes may not be accelerated because of the occurrence of certain specified events of default.

To exercise either defeasance option as to each series of the notes, we must irrevocably deposit in trust with the trustee money and/or obligations backed by the full faith and credit of the United States that will provide money in an amount sufficient without reinvestment, in the written opinion of a nationally recognized firm of independent public accountants, to pay the principal of, premium, if any, and each installment of interest on the notes.

We may only establish this trust if, among other things:

Governing Law

New York law will govern the indenture and the notes.

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The Trustee

The Bank of New York Mellon Trust Company, N.A. is the trustee under the indenture. The Bank of New York Mellon Trust Company, N.A. and its affiliates perform certain commercial banking services for some of our affiliates for which they receive customary fees.

If an event of default occurs and is continuing, the trustee shall exercise such of the rights and powers vested in it by the indenture, and use the same degree of care and skill in their exercise, as a prudent person would exercise or use under the circumstances in the conduct of his own affairs. Subject to the provisions of the indenture, the trustee will become obligated to exercise any of its powers under the indenture at the request of any of the holders of any notes only after those holders have offered the trustee security or indemnity satisfactory to it.

The indenture limits the right of the trustee, if it is one of our creditors, to obtain payment of claims or to realize on certain property received for any such claim, as security or otherwise. The trustee may engage in other transactions with us. If, after the occurrence of a default under the indenture, it acquires any conflicting interest within the meaning of the Trust Indenture Act of 1939, as amended, however, it must eliminate that conflict or resign within 90 days after ascertaining that it has a conflicting interest, unless the default has been cured, waived or otherwise eliminated within the 90-day period.

Book-Entry; Delivery and Form

Except as set forth below, each series of the notes will be issued in registered global form in minimum denominations of $2,000 and multiples of $1,000 in excess of that amount.

Each series of the notes will initially be represented by one or more fully registered global notes, which we refer to collectively as the “global notes.” Each such global note will be deposited upon issuance with the trustee as custodian for DTC in New York, New York, and registered in the name of DTC or its nominee, in each case for credit to an account of a direct or indirect participant in DTC as described below. Transfers of beneficial interests in the global notes will be subject to the applicable rules and procedures of DTC and its direct or indirect participants (including, if applicable, those of Euroclear and Clearstream), which may change from time to time.

The following are summaries of certain rules and operating procedures of DTC that affect the payment of principal and interest and the transfers of interests in the global notes. Each series of the notes will be issued only in the form of definitive global securities that will be deposited with, or on behalf of, DTC and registered in the name of Cede & Co., as nominee of DTC. Unless and until they are exchanged in whole or in part for notes in definitive form under the limited circumstances described below, a global note may not be transferred except as a whole (1) by DTC to a nominee, (2) by a nominee of DTC to DTC or another nominee of DTC or (3) by DTC or any such nominee to a successor of DTC or a nominee of such successor. Accountholders in the Euroclear or Clearstream Banking clearance systems may hold beneficial interests in the notes through the accounts that each of these systems maintain as participants in DTC.

Ownership of beneficial interests in the global notes will be limited to persons that have accounts with DTC for such global notes, who we refer to as “participants,” or persons that may hold interests through participants.

Upon the issuance of the global notes, DTC will credit, on its book-entry registration and transfer system, the participants’ accounts with the respective principal amounts of the notes represented by such global notes beneficially owned by such participants. Ownership of beneficial interests in the global notes will be shown on, and the transfer of such ownership interests will be effected only through, records maintained by DTC (with respect to interests of participants). Beneficial owners will not receive written confirmation from DTC of their purchase. Beneficial owners are, however, expected to receive written confirmations providing details of the

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transaction, as well as periodic statements of their holdings, from the participant through which the beneficial owner entered into the transaction. Transfers of ownership interests in the global notes are to be accomplished by entries made on the books of participants acting on behalf of beneficial owners. Beneficial owners will not receive certificates representing their ownership interest in the global notes, except in the event that use of the book-entry system for the global notes is discontinued. The laws of some states may require that certain purchasers of securities take physical delivery of such securities in definitive form. Such laws may limit or impair the ability to own, transfer or pledge beneficial interests in the global notes.

So long as DTC or its nominee is the registered owner of the global notes, DTC or its nominee, as the case may be, will be considered the sole owner or holder of the notes represented by such global notes for all purposes under the indenture. Except as set forth below, owners of beneficial interests in the global notes will not be entitled to have notes represented by such global notes registered in their names, will not receive or be entitled to receive physical delivery of such notes in certificated form and will not be considered the registered owners or holders thereof under the indenture. Accordingly, each person owning a beneficial interest in the global notes must rely on the procedures of DTC and, if such person is not a participant, on the procedures of the participant through which such person owns its interest, to exercise any rights of a holder under the indenture. We understand that under existing industry practices, if we request any action of holders or if an owner of a beneficial interest in any of the global notes desires to give or take any action that a holder is entitled to give or take under the indenture, DTC would authorize the participants holding the relevant beneficial interests to give or take such action, and such participants would authorize beneficial owners owning through such participants to give or to take such action or would otherwise act upon the instructions of beneficial owners holding through them.

Conveyance of notices and other communications by DTC to direct participants, by direct participants to indirect participants, and by direct participants and indirect participants to beneficial owners will be governed by arrangements among them, subject to any statutory or regulatory requirements as may be in effect from time to time.

Principal and interest payments on interests represented by the global notes will be made to DTC or its nominee, as the case may be, as the registered owner of such global notes. None of MPLX LP, the trustee or any other agent of MPLX LP or agent of the trustee will have any responsibility or liability for any facet of the records relating to or payments made on account of beneficial ownership of interests. We expect that DTC, upon receipt of any payment of principal or interest in respect of the global notes, will immediately credit participants’ accounts with payments in amounts proportionate to their respective beneficial interests in such global notes as shown on the records of DTC. We also expect that payments by participants to owners of beneficial interests in the global notes held through such participants will be governed by standing customer instructions and customary practice, as is now the case with securities held for the accounts of customers in bearer form or registered in “street name,” and will be the responsibility of such participants.

If DTC is at any time unwilling or unable to continue as depository for the global notes, and we fail to appoint a successor depository registered as a clearing agency under the Exchange Act within 90 days, we will issue notes in definitive form in exchange for the global notes for each series of the notes. Any notes issued in definitive form in exchange for such global notes will be registered in such name or names, and will be issued in denominations of $2,000 and integral multiples of $1,000 in excess thereof as DTC shall instruct the trustee. It is expected that such instructions will be based upon directions received by DTC from participants with respect to ownership of beneficial interests in the global notes.

DTC has advised us that DTC is a limited purpose trust company organized under the Banking Law of the State of New York, a “banking organization” within the meaning of the New York Banking Law, a member of the Federal Reserve System, a “clearing corporation” within the meaning of the New York Uniform Commercial Code and a “clearing agency” registered pursuant to the provisions of Section 17A of the Exchange Act. DTC was created to hold the securities of its participants and to facilitate the clearance and settlement of transactions

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among its participants in such securities through electronic book-entry changes in accounts of the participants, thereby eliminating the need for physical movement of securities certificates. DTC’s participants include securities brokers and dealers, banks, trust companies, clearing corporations and certain other organizations, some of which (and/or their representatives) directly or indirectly own DTC. Access to the DTC book-entry system is also available to others, such as banks, brokers and dealers and trust companies that clear through or maintain a custodial relationship with a participant, either directly or indirectly.

Same-Day Settlement and Payment

All payments of principal and interest on the notes will be made by MPLX LP in immediately available funds. The notes will trade in DTC’s Same-Day Funds Settlement System until maturity, and secondary market trading activity in the notes will therefore be required by DTC to settle in immediately available funds.

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SUPPLEMENTAL INFORMATION REGARDING OUR PARTNERSHIP AGREEMENT AND PROVISIONS OF OUR PARTNERSHIP AGREEMENT RELATING TO CASH DISTRIBUTIONS

In connection with the GP/IDR Restructuring, our general partner amended and restated our partnership agreement by entering into a Fourth Amended and Restated Agreement of Limited Partnership of MPLX LP, dated as of February 1, 2018, which we refer to as the amended and restated partnership agreement. The amended and restated partnership agreement reflects the cancellation of previously outstanding incentive distribution rights in us and the conversion of our general partner’s economic general partner interest in us into a non-economic general partner interest in the GP/IDR Restructuring. In addition, the amended and restated partnership agreement reflects the conversion of the last remaining outstanding Class B units into common units effective on July 1, 2017.

The amended and restated partnership agreement revised the provisions of the previously effective partnership agreement relating to cash distributions by removing provisions providing for distributions of available cash to the holders of incentive distribution rights and to our general partner on its general partner interest. Except as otherwise provided under the amended and restated partnership agreement, we will distribute available cash as of the end of each quarter, after payment of distributions to the holders of Series A Preferred units, pro rata to our limited partners (excluding the holders of Series A Preferred units) as of the record date selected by our general partner.

For the full text of the amended and restated partnership agreement, please see exhibit 3.1 to our Current Report on Form 8-K filed on February 2, 2018.

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MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES

The following is a summary of material U.S. federal income tax considerations with respect to the acquisition, ownership and disposition of the notes, but it does not purport to be a complete analysis of all the potential tax considerations relating to the acquisition, ownership and disposition of the notes. This summary is based upon the provisions of the Internal Revenue Code of 1986, as amended, which we refer to as the “Code,” applicable U.S. Treasury Regulations promulgated thereunder, administrative rulings and judicial decisions, all as of the date of this prospectus supplement. These authorities may be changed or subject to differing interpretations, possibly with retroactive effect. We have not obtained, nor do we intend to obtain, a ruling from the IRS with respect to the statements made in this summary and there can be no assurance that the IRS will agree with such statements or that a court would not sustain a challenge by the IRS in the event of litigation.

This summary is limited to beneficial owners of the notes, which we refer to in this section as “Holders,” that purchase the notes upon their initial issuance at their “initial offering price” (i.e., the first price at which a substantial amount of the notes is sold for cash to investors (excluding sales to bond houses, brokers or similar persons or organizations acting in the capacity as underwriters, placement agents or wholesalers)) and that will hold the notes as “capital assets” within the meaning of Section 1221 of the Code (generally, property held for investment). This summary does not address the tax considerations arising under the laws of any foreign, state, local or other jurisdiction. In addition, this summary does not address any U.S. federal tax considerations other than U.S. federal income tax considerations that may be relevant to Holders’ particular circumstances, or to certain categories of Holders that may be subject to special rules, such as:

If an entity or arrangement treated as a partnership for U.S. federal income tax purposes holds notes, the U.S. federal income tax treatment of a partner in such partnership generally will depend upon the status of the partner and the activities of the partnership. If you are a partnership or a partner in a partnership that will hold notes, you are urged to consult your own tax advisor regarding the tax consequences to you of acquiring, holding and disposing of the notes.

This summary of certain U.S. federal income tax considerations is for general information only and is not tax advice. You are urged to consult your tax advisor with respect to the application of U.S. federal income tax

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laws to your particular situation as well as any tax considerations arising under other U.S. federal tax laws (such as the estate or gift tax laws) or under the laws of any state, local, foreign or other taxing jurisdiction or under any applicable tax treaty.

Considerations for U.S. Holders

The following discussion is a summary of the general U.S. federal income tax consequences that will apply to you if you are a “U.S. Holder.” For purposes of this discussion, a U.S. Holder is a beneficial owner of a note that is, for U.S. federal income tax purposes:

Payments of interest

It is anticipated, and this discussion assumes, that the notes will be issued at par or at a discount that is less than a statutorily defined “de minimis” amount of original issue discount for U.S. federal income tax purposes. Stated interest on the notes will generally be taxable to you as ordinary income at the time it is paid or accrued in accordance with your method of accounting for U.S. federal income tax purposes.

Sale or other taxable disposition of notes

Upon the sale, exchange, redemption, retirement or other taxable disposition of a note, you will recognize taxable gain or loss equal to the difference between the amount realized on such disposition (except to the extent any amount realized is attributable to accrued but unpaid interest, which, if not previously included in income, will be treated as interest as described above) and your adjusted tax basis in the note. Your adjusted tax basis in a note generally will be your cost for the note. Gain or loss recognized on the disposition of a note generally will be capital gain or loss, and will be long-term capital gain or loss if, at the time of such disposition, your holding period for the note is more than 12 months. Long-term capital gains of non-corporate taxpayers are generally eligible for preferential rates of taxation. The deductibility of capital losses is subject to certain limitations.

Additional Medicare tax

An additional 3.8% Medicare tax is imposed on the “net investment income” of certain U.S. citizens and resident aliens, and on the undistributed “net investment income” of certain estates and trusts. Among other items, “net investment income” generally includes gross income from interest, and certain net gain from the sale, redemption, exchange, retirement or other taxable disposition of property, such as the notes, less certain deductions. You are urged to consult your own tax advisor with respect to the Medicare tax and its applicability in your particular circumstances to income and gains in respect of an investment in the notes.

Information reporting and backup withholding

In general, information reporting requirements will apply to payments of interest and the proceeds of certain sales and other taxable dispositions (including retirements or redemptions) of notes unless you are an exempt

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recipient. Backup withholding (currently at a rate of 24%) will apply to such payments if you fail to provide your taxpayer identification number or certification of exempt status or have been notified by the IRS that payments to you are subject to backup withholding. Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules will generally be allowed as a credit against your U.S. federal income tax liability and may entitle you to a refund, provided that you furnish the required information to the IRS on a timely basis.

Considerations for Non-U.S. Holders

The following is a summary of the general U.S. federal income tax consequences that will apply to you if you are a “Non-U.S. Holder” of the notes. You are a “Non-U.S. Holder” if you are a beneficial owner of a note that is an individual, corporation, estate or trust and that is not a U.S. Holder.

Payments of interest

Subject to the discussion of backup withholding and FATCA withholding below, payments of interest on the notes to you generally will be exempt from U.S. federal income tax and withholding tax under the “portfolio interest” exemption if you properly certify as to your foreign status (as described below) and:

If you cannot satisfy the requirements described above for the portfolio interest exemption, payments of interest made to you on the notes will be subject to the 30% U.S. federal withholding tax, unless you provide us either with (1) a properly executed IRS Form W-8BEN or IRS Form W-8BEN-E (or appropriate substitute or successor form) establishing an exemption from (or a reduction of) withholding under the benefit of an applicable income tax treaty or (2) a properly executed IRS Form W-8ECI (or appropriate substitute or successor form) certifying that interest paid on the note is not subject to withholding tax because the interest is effectively connected with your conduct of a trade or business in the United States (as discussed below under “—Income or gain effectively connected with a United States trade or business”).

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Sale or other taxable disposition of notes

Subject to the discussion of backup withholding and FATCA withholding below, you generally will not be subject to U.S. federal income or withholding tax on any gain realized on the sale, exchange, redemption, retirement or other taxable disposition of a note unless:

If a Non-U.S. Holder is described in the first bullet point, see “—Income or gain effectively connected with a United States trade or business” below. If you are described in the second bullet point, you will generally be subject to U.S. federal income tax at a rate of 30% on the amount by which your capital gains allocable to United States sources, including gain from such disposition, exceed any capital losses allocable to United States sources, except as otherwise required by an applicable income tax treaty.

To the extent that the amount realized on a sale, redemption, exchange, retirement or other taxable disposition of the notes is attributable to accrued but unpaid interest on the notes, this amount generally will be treated in the same manner as described in “—Payments of interest” above.

Income or gain effectively connected with a United States trade or business

If you are engaged in the conduct of a trade or business in the United States and interest on a note or gain recognized from the sale, exchange, redemption, retirement or other taxable disposition of a note is effectively connected with the conduct of that trade or business, you will generally be subject to U.S. federal income tax (but not the 30% U.S. federal withholding tax on interest if certain certification requirements are satisfied) on that interest and on gain on a net income basis in the same manner as if you were a United States person as defined under the Code. You can generally meet these certification requirements by providing a properly executed IRS Form W-8ECI or appropriate substitute form to us or our paying agent. If you are eligible for the benefits of an income tax treaty between the United States and your country of residence, any effectively connected income or gain generally will be subject to U.S. federal income tax only if it is also attributable to a permanent establishment or fixed base maintained by you in the United States. In addition, if you are a foreign corporation, you may be subject to an additional branch profits tax equal to 30% (or a lower applicable income tax treaty rate) of your earnings and profits for the taxable year, subject to adjustments, that are effectively connected with your conduct of a trade or business in the United States.

Information reporting and backup withholding

Generally, information returns will be filed with the IRS in connection with payments of interest on the notes and proceeds from the sale or other taxable disposition (including a retirement or redemption) of the notes. Copies of the information returns reporting such payments and any withholding may also be made available to the tax authorities in the country in which you reside under the provisions of an applicable income tax treaty. You may be subject to backup withholding of tax on payments of interest and, depending on the circumstances, the proceeds of a sale or other taxable disposition (including a retirement or redemption) unless you comply with certain certification procedures to establish that you are not a U.S. person. The certification procedures required to claim an exemption from withholding of tax on interest described above generally will satisfy the certification requirements necessary to avoid backup withholding as well. Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules will generally be allowed as a credit against your U.S. federal income tax liability and may entitle you to a refund, provided that you furnish the required information to the IRS on a timely basis. You are urged to consult your own tax advisor regarding the application of backup withholding rules in your particular situation, the availability of an exemption from backup withholding and the procedure for obtaining such an exemption, if applicable.

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FATCA withholding

Sections 1471 through 1474 of the Code and the Treasury Regulations and administrative guidance issued thereunder, which we refer to as “FATCA,” impose a 30% withholding tax on any U.S.-source interest paid on debt obligations, such as the notes, and beginning after December 31, 2018 on the gross proceeds from a disposition of such obligations, in each case, if paid to a “foreign financial institution” or a “non-financial foreign entity” (each as defined in the Code), including when acting as an intermediary, unless: (i) in the case of a foreign financial institution, such institution enters into an agreement with the IRS to withhold on certain payments, and to collect and provide to the IRS information regarding U.S. account holders of such institution (which includes certain equity and debt holders of such institution, as well as certain account holders that are non-U.S. entities with United States owners); (ii) in the case of a non-financial foreign entity, such entity certifies that it does not have any “substantial United States owners” (as defined in the Code) or provides the withholding agent with a certification identifying its direct and indirect substantial United States owners; or (iii) the foreign financial institution or non-financial foreign entity otherwise qualifies for an exemption from these rules. Foreign financial institutions located in jurisdictions that have an intergovernmental agreement with the United States with respect to these rules may be subject to different rules. Under certain circumstances, a Holder might be eligible for refunds or credits of such taxes. The rules under FATCA are new and complex. If you hold the notes through a non-U.S. intermediary or if you are a Non-U.S. Holder, you are encouraged to consult with your own tax advisor regarding the implications of FATCA on an investment in the notes.

The discussion of U.S. federal income tax considerations set forth above is included for general information only and is not tax advice. Prospective purchasers of the notes are urged to consult their own tax advisors with respect to the particular tax consequences to them of the purchase, ownership and disposition of notes, including the tax consequences under U.S. federal, state, local, foreign and other tax laws and the possible effects of changes in applicable tax laws.

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CERTAIN ERISA CONSIDERATIONS

The following summary regarding certain aspects of the Employee Retirement Income Security Act of 1974, which we refer to as “ERISA,” and the Code is based on ERISA and the Code, judicial decisions and United States Department of Labor and IRS regulations and rulings that are in existence on the date of this prospectus supplement. This summary is general in nature and does not address every issue pertaining to ERISA or the Code that may be applicable to us, the notes or a particular investor. Accordingly, each prospective investor should consult with his, her or its own counsel in order to understand the issues relating to ERISA and the Code that affect or may affect the investor with respect to this investment.

ERISA and the Code impose certain requirements on employee benefit plans that are subject to Title I of ERISA and plans subject to Section 4975 of the Code, each such employee benefit plan or plan we refer to as a “Plan,” on entities whose underlying assets include plan assets by reason of a Plan’s investment in such entities and on those persons who are “fiduciaries” as defined in Section 3(21) of ERISA and Section 4975 of the Code with respect to Plans. In considering an investment of the assets of a Plan subject to Part 4 of Subtitle B of Title I of ERISA in the notes, a fiduciary must, among other things, discharge its duties solely in the interest of the participants of such Plan and their beneficiaries and for the exclusive purpose of providing benefits to such participants and beneficiaries and defraying reasonable expenses of administering the Plan. A fiduciary must act prudently and must diversify the investments of a Plan subject to Part 4 of Subtitle B of Title I of ERISA so as to minimize the risk of large losses, as well as discharge its duties in accordance with the documents and instruments governing such Plan. In addition, ERISA generally requires fiduciaries to hold all assets of a Plan subject to Part 4 of Subtitle B of Title I of ERISA in trust and to maintain the indicia of ownership of such assets within the jurisdiction of the district courts of the United States. A fiduciary of a Plan subject to Part 4 of Subtitle B of Title I of ERISA should consider whether an investment in the notes satisfies these requirements.

An investor who is considering acquiring the notes with the assets of a Plan must consider whether the acquisition and holding of the notes will constitute or result in a non-exempt prohibited transaction. Section 406(a) of ERISA and Sections 4975(c)(1)(A), (B), (C) and (D) of the Code prohibit certain transactions that involve a Plan and a “party in interest” as defined in Section 3(14) of ERISA or a “disqualified person” as defined in Section 4975(e)(2) of the Code with respect to such Plan. Examples of such prohibited transactions include, but are not limited to, sales or exchanges of property (such as the notes) or extensions of credit between a Plan and a party in interest or disqualified person. Section 406(b) of ERISA and Sections 4975(c)(1)(E) and (F) of the Code generally prohibit a fiduciary with respect to a Plan from dealing with the assets of the Plan for its own benefit (for example when a fiduciary of a Plan uses its position to cause the Plan to make investments in connection with which the fiduciary (or a party related to the fiduciary) receives a fee or other consideration).

ERISA and the Code contain certain exemptions from the prohibited transactions described above, and the Department of Labor has issued several exemptions, although certain exemptions do not provide relief from the prohibitions on self-dealing contained in Section 406(b) of ERISA and Sections 4975(c)(1)(E) and (F) of the Code. Exemptions include Section 408(b)(17) of ERISA and Section 4975(d)(20) of the Code pertaining to certain transactions with non-fiduciary service providers; Department of Labor Prohibited Transaction Class Exemption 95-60, which we refer to as a “PTCE,” applicable to transactions involving insurance company general accounts; PTCE 90-1, regarding investments by insurance company pooled separate accounts; PTCE 91-38, regarding investments by bank collective investment funds; PTCE 84-14, regarding investments effected by a qualified professional asset manager; and PTCE 96-23, regarding investments effected by an in-house asset manager. There can be no assurance that any of these exemptions will be available with respect to the acquisition of the notes. Under Section 4975 of the Code, excise taxes are imposed on disqualified persons who participate in non-exempt prohibited transactions (other than a fiduciary acting only as such) and such transactions may have to be rescinded.

As a general rule, a governmental plan, as defined in Section 3(32) of ERISA, each such plan we refer to as a “Governmental Plan,” a church plan, as defined in Section 3(33) of ERISA, that has not made an election under

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Section 410(d) of the Code, each such plan we refer to as a “Church Plan,” and a plan maintained outside the United States primarily for the benefit of persons substantially all of whom are nonresident aliens, each such plan we refer to as a “non-U.S. Plan,” are not subject to Title I of ERISA or Section 4975 of the Code. Accordingly, assets of such plans may be invested without regard to the fiduciary and prohibited transaction considerations described above. Although a Governmental Plan, a Church Plan or a non-U.S. Plan is not subject to Title I of ERISA or Section 4975 of the Code, it may be subject to other United States federal, state or local laws or non-U.S. laws that regulate its investments, any of which we refer to as a “Similar Law.” A fiduciary of a Government Plan, a Church Plan or a non-U.S. Plan should consider whether investing in the notes satisfies the requirements, if any, under any applicable Similar Law.

The notes may be acquired by a Plan, a Governmental Plan, a Church Plan, a non-U.S. Plan or an entity whose underlying assets include the assets of a Plan, but only if the acquisition will not result in a nonexempt prohibited transaction under ERISA or Section 4975 of the Code or a violation of Similar Law. Therefore, any investor in the notes will be deemed to represent and warrant to us and the trustee that (1)(a) it is not (i) a Plan, (ii) a Governmental Plan, (iii) a Church Plan, (iv) a non-U.S. Plan or (v) an entity whose underlying assets include the assets of a Plan, (b) it is a Plan or an entity whose underlying assets include the assets of a Plan and the acquisition and holding of the notes will not result in a nonexempt prohibited transaction under Section 406 of ERISA or Section 4975 of the Code, or (c) it is a Governmental Plan, a Church Plan or a non-U.S. Plan that is not subject to (i) ERISA, (ii) Section 4975 of the Code or (iii) any Similar Law that prohibits or imposes excise or penalty taxes on the acquisition or holding of the notes; and (2) it will notify us and the trustee immediately if, at any time, it is no longer able to make the representations contained in clause (1) above. Any purported transfer of the notes to a transferee that does not comply with the foregoing requirements shall be null and void ab initio.

In addition, each investor that is a Plan or whose underlying assets include the assets of a Plan, by acceptance of the notes, will be deemed to have represented and warranted that a fiduciary acting on its behalf is causing it to purchase the notes and that such fiduciary: (1) is a bank, an insurance carrier, a registered investment adviser, a registered broker-dealer or an independent fiduciary with at least $50 million of assets under management or control as specified in 29 CFR Section 2510.3-21(c)(1)(i) (excluding an IRA owner if the purchaser is an IRA); (2) is independent (for purposes of 29 CFR Section 2510.3-21(c)(1)) of MPLX LP, each underwriter and their respective affiliates (the “Transaction Parties”); (3) is capable of evaluating investment risks independently, both in general and with regard to particular transactions and investment strategies, including the purchaser’s transactions with the Transaction Parties hereunder; (4) has been advised that none of the Transaction Parties has undertaken or will undertake to provide impartial investment advice, or has given or will give advice in a fiduciary capacity, in connection with the purchaser’s transactions with the Transaction Parties contemplated hereby; (5) is a “fiduciary” under Section 3(2 l)(A) of ERISA or Section 4975(e)(3) of the Code, or both, as applicable, with respect to, and is responsible for exercising independent judgment in evaluating, the purchaser’s transactions with the Transaction Parties contemplated hereby; and (6) understands and acknowledges the existence and nature of the underwriting discounts, commissions and fees, and any other related fees, compensation arrangements or financial interests, described in this offering memorandum; and understands, acknowledges and agrees that no such fee or other compensation is a fee or other compensation for the provision of investment advice, and that none of the Transaction Parties, nor any of their respective directors, officers, members, partners, employees, principals or agents has received or will receive a fee or other compensation from the purchaser or such fiduciary for the provision of investment advice (rather than other services) in connection with the purchaser’s transactions with the Transaction Parties contemplated hereby.

This offer is not a representation by us or the underwriters that an acquisition of the notes meets any or all legal requirements applicable to investments by Plans, Governmental Plans, Church Plans, non-U.S. Plans or entities whose underlying assets include the assets of a Plan or that such an investment is appropriate for any particular Plan, Governmental Plan, Church Plan, non-U.S. Plan or entity whose underlying assets include the assets of a Plan.

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UNDERWRITING (CONFLICTS OF INTEREST)

Merrill Lynch, Pierce, Fenner & Smith Incorporated, Barclays Capital Inc., Mizuho Securities USA LLC, J.P. Morgan Securities LLC, MUFG Securities Americas Inc. and Wells Fargo Securities, LLC are acting as representatives of the underwriters. We and the underwriters named below have entered into an underwriting agreement with respect to the notes. Subject to certain conditions, the underwriters have severally agreed to purchase the principal amount of notes indicated opposite their name in the following table.

The underwriters are committed to take and pay for all of the notes being offered, if any are taken.

Notes sold by the underwriters to the public will initially be offered at the public offering prices set forth on the cover of this prospectus supplement. The offering of the notes by the underwriters is subject to receipt and acceptance and subject to the underwriters’ right to reject any order in whole or in part. After the initial offering of the notes, the offering prices at which the notes are being offered may be changed at any time without notice.

The notes are a new issue of securities. We have been advised by the underwriters that the underwriters intend to make a market in the notes but are not obligated to do so and may discontinue market making at any time without notice. No assurance can be given as to the liquidity of the trading market for the notes.

In connection with the offering, the underwriters may purchase and sell notes in the open market. These transactions may include short sales, stabilizing transactions and purchases to cover positions created by short sales. Short sales involve the sale by the underwriters of a greater number of notes than they are required to purchase in the offering. Stabilizing transactions consist of certain bids or purchases made for the purpose of preventing or retarding a decline in the market prices of the notes while the offering is in progress.

The underwriters also may impose a penalty bid. This occurs when a particular underwriter repays to another underwriter a portion of the underwriting discount received by it because such other underwriter has repurchased notes sold by or for the account of such underwriter in stabilizing or short covering transactions.

These activities by the underwriters, as well as other purchases by the underwriters for their own accounts, may stabilize, maintain or otherwise affect the market prices of the notes. As a result, the prices of the notes may

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be higher than the prices that otherwise might exist in the open market. If these activities are commenced, they may be discontinued by the underwriters at any time. These transactions may be effected in the over-the-counter market or otherwise.

The following table shows the underwriting discounts that we will pay to the underwriters in connection with this offering, expressed as a percentage of the principal amount of the notes and in total:

We estimate that our share of the total expenses of the offering, excluding underwriting discounts, will be approximately $        million.

It is expected that delivery of the notes will be made, against payment for the notes, on or about February     , 2018, which will be the third business day following the pricing of the notes. Purchasers of the notes who wish to trade the notes on the date of this prospectus supplement will be required, because the notes initially will settle within three business days (T+3), to specify an alternate settlement cycle at the time of any such trade to prevent a failed settlement. Purchasers of the notes who wish to trade on the date of this prospectus supplement should consult their own legal advisors.

Prohibition of Sales to EEA Retail Investors

The notes are not intended to be offered, sold or otherwise made available to and should not be offered, sold or otherwise made available to any retail investor in the European Economic Area. For these purposes:

a retail investor means a person who is one (or more) of:

Consequently, no key information document required by Regulation (EU) No 1286/2014 (as amended, the “PRIIPs Regulation”) for offering or selling the notes or otherwise making them available to retail investors in the European Economic Area has been prepared and therefore offering or selling the notes or otherwise making them available to any retail investor in the European Economic Area may be unlawful under the PRIIPs Regulation.

This prospectus supplement and the accompanying prospectus have been prepared on the basis that any offer of notes in any Member State of the European Economic Area will be made pursuant to an exemption under the Prospectus Directive from the requirement to publish a prospectus for offers of notes. This prospectus supplement and the accompanying prospectus are not a prospectus for the purposes of the Prospectus Directive.

Notice to Prospective Investors in the United Kingdom

Each of the underwriters severally represents warrants and agrees as follows:

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Notice to Prospective Investors in Hong Kong

The notes have not been offered or sold and will not be offered or sold in Hong Kong, by means of any document, other than (i) in circumstances which do not constitute an offer to the public within the meaning of the Companies (Winding Up and Miscellaneous Provisions) Ordinance (Cap. 32 of the Laws of Hong Kong), or (ii) to “professional investors” within the meaning of the Securities and Futures Ordinance (Cap. 571 of the Laws of Hong Kong) and any rules made thereunder, or (iii) in other circumstances which do not result in the document being a “prospectus” within the meaning of the Companies (Winding Up and Miscellaneous Provisions) Ordinance (Cap. 32 of the Laws of Hong Kong). No advertisement, invitation or document relating to the notes has been issued or will be issued or has been or will be in the possession of any person for the purpose of issue (in each case whether in Hong Kong or elsewhere), which is directed at, or the contents of which are likely to be accessed or read by, the public in Hong Kong (except if permitted to do so under the securities laws of Hong Kong) other than with respect to notes which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” within the meaning of the Securities and Futures Ordinance (Cap. 571 of the Laws of Hong Kong) and any rules made thereunder.

Notice to Prospective Investors in Japan

The notes offered in this prospectus supplement have not been and will not be registered under the Financial Instruments and Exchange Law of Japan (Law No. 25 of 1948, as amended)(the “FIEL”), and the notes have not been offered or sold and will not be offered or sold, directly or indirectly, in Japan or to or for the account of any resident of Japan or to others for re-offering or resale, directly or indirectly, in Japan or to or for the account of any resident of Japan (for the purposes of this paragraph, “resident of Japan” shall mean any person resident in Japan, including any corporation or other entity organized under the laws of Japan), except (i) pursuant to an exemption from the registration requirements of the FIEL and (ii) in compliance with any other applicable requirements of Japanese law.

Notice to Prospective Investors in Switzerland

This document is not intended to constitute an offer or solicitation to purchase or invest in the notes described herein. The notes may not be publicly offered, sold or advertised, directly or indirectly, in, into or from Switzerland and will not be listed on the SIX Swiss Exchange or on any other exchange or regulated trading facility in Switzerland. Neither this document nor any other offering or marketing material relating to the notes constitutes a prospectus as such term is understood pursuant to article 652a or article 1156 of the Swiss Code of Obligations or a listing prospectus within the meaning of the listing rules of the SIX Swiss Exchange or any other regulated trading facility in Switzerland, and neither this document nor any other offering or marketing material relating to the notes may be publicly distributed or otherwise made publicly available in Switzerland. Neither this document nor any other offering or marketing material relating to the offering, nor the Company nor the notes have been or will be filed with or approved by any Swiss regulatory authority. The notes are not subject to the supervision by any Swiss regulatory authority, e.g., the Swiss Financial Markets Supervisory Authority FINMA (‘‘FINMA’’), and investors in the notes will not benefit from protection or supervision by such authority.

Notice to Prospective Investors in Singapore

This prospectus supplement has not been, and will not be, registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this offering memorandum and any other document or material in

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connection with the offer or sale, or invitation for subscription or purchase, of the notes may not be circulated or distributed, nor may the notes be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor as defined in Section 4A of the Securities and Futures Act, Chapter 289 of Singapore (the “SFA”)) pursuant to Section 274 of the SFA, (ii) to a relevant person (as defined in Section 275(2) of the SFA) pursuant to Section 275(1), or any person pursuant to Section 275(1A), and in accordance with the conditions specified in Section 275 of the SFA or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA, in each case subject to compliance with conditions set forth in the SFA.

Where the notes are subscribed or purchased under Section 275 of the SFA by a relevant person which is:

Notice to Prospective Investors in Taiwan

The notes have not and will not be registered or filed with, or approved by, the Financial Supervisory Commission of Taiwan pursuant to relevant securities laws and regulations and may not be sold, issued, or offered within Taiwan through a public offering or in circumstances which constitute an offer within the meaning of the Securities and Exchange Act of Taiwan that requires a registration or filing with or approval of the Financial Supervisory Commission of Taiwan. No person or entity in Taiwan has been authorized or will be authorized to offer, sell, give advice regarding or otherwise intermediate the offering and sale of the notes in Taiwan.

Other Matters Relating to the Underwriters

We have agreed to indemnify the several underwriters against certain liabilities, including liabilities under the Securities Act, and to contribute to payments that the underwriters may be required to make in respect of those liabilities.

The underwriters and their respective affiliates are full service financial institutions engaged in various activities, which may include sales and trading, commercial and investment banking, advisory, investment management, investment research, principal investment, hedging, market making, brokerage and other financial and non-financial activities and services. Certain of the underwriters and their respective affiliates have provided, and may in the future provide, a variety of these services to us and to persons and entities with relationships with

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us, for which they received or will receive customary fees and expenses. Affiliates of certain of the underwriters are lenders under the credit facility discussed under “Description of Other Indebtedness,” for which they have received, and in the future would receive, customary fees.

In the ordinary course of their various business activities, the underwriters and their respective affiliates, officers, directors and employees may purchase, sell or hold a broad array of investments and actively trade securities, derivatives, loans, commodities, currencies, credit default swaps and other financial instruments for their own account and for the accounts of their customers, and such investment and trading activities may involve or relate to assets, securities and/or instruments of us (directly, as collateral securing other obligations or otherwise) and/or persons and entities with relationships with us. The underwriters and their respective affiliates may also communicate independent investment recommendations, market color or trading ideas and/or publish or express independent research views in respect of such assets, securities or instruments and may at any time hold, or recommend to clients that they should acquire, long and/or short positions in such assets, securities and instruments.

Certain of the underwriters or their affiliates have a lending relationship with us. Certain of those underwriters or their affiliates routinely hedge, and certain other of those underwriters or their affiliates may hedge, their credit exposure to us consistent with their customary risk management policies. Typically, such underwriters and their affiliates would hedge such exposure by entering into transactions which consist of either the purchase of credit default swaps or the creation of short positions in our securities, including potentially the notes offered hereby. Any such credit default swaps or short positions could adversely affect future trading prices of the notes offered hereby.

Conflicts of Interest

Certain of the underwriters or their affiliates are lenders under our credit facilities and will receive a portion of the net proceeds of this offering used to repay amounts outstanding under the credit facilities. At least 5% of the net proceeds of this offering may be directed to one or more of the underwriters (or their affiliates). The receipt of at least 5% of the net proceeds of this offering by any underwriter (or its affiliates) would be considered a “conflict of interest” under FINRA Rule 5121. As such, this offering is being conducted in accordance with the applicable requirements of Rule 5121 regarding the underwriting of securities of a company with a member that has a conflict of interest within the meaning of those rules. Rule 5121 requires prominent disclosure of the nature of the conflict of interest in the prospectus supplement for the public offering. Pursuant to Rule 5121(a)(1)(C), the appointment of a qualified independent underwriter is not necessary in connection with this offering as the securities offered are investment grade rated.

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LEGAL MATTERS

Jones Day will pass upon the validity of the notes being offered hereby. The underwriters have been represented in connection with this offering by Cravath, Swaine & Moore LLP.

EXPERTS

The consolidated financial statements incorporated in this Prospectus by reference to MPLX LP’s Current Report on Form 8-K dated May 1, 2017 and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Control over Financial Reporting) incorporated in this Prospectus by reference to the Annual Report on Form 10-K of MPLX LP for the year ended December 31, 2016 have been so incorporated in reliance on the report, which contains an explanatory paragraph on the effectiveness of internal control over financial reporting due to the exclusion of certain elements of the internal control over financial reporting of the Hardin Street Transportation LLC, Woodhaven Cavern LLC and MPLX Terminals LLC businesses MPLX LP acquired during 2017, of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

The audited combined historical financial statements of Hardin Street Transportation LLC and Woodhaven Cavern LLC included in Exhibit 99.1 of MPLX LP’s Current Report on Form 8-K dated March 2, 2017 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

The audited consolidated historical financial statements of MPLX Terminals LLC included in Exhibit 99.2 of MPLX LP’s Current Report on Form 8-K dated March 2, 2017 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

The consolidated financial statements, incorporated in this prospectus supplement by reference from the MarkWest Energy Partners, L.P.’s Annual Report on Form 10-K for the year ended December 31, 2014, have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their report, which is incorporated herein by reference. Such consolidated financial statements have been so incorporated in reliance upon the report of such firm given upon their authority as experts in accounting and auditing.

The audited financial statements of Explorer Pipeline Company as of December 31, 2016 and 2015 included in Exhibit 99.1 of MPLX LP’s Current Report on Form 8-K dated September 1, 2017 and incorporated by reference in this prospectus and elsewhere in the registration statement have been so incorporated by reference in reliance upon the report of Grant Thornton LLP, independent certified public accountants, upon the authority of said firm as experts in accounting and auditing.

The audited consolidated statements of income and retained earnings, comprehensive income and cash flows of Explorer Pipeline Company for the year ended December 31, 2014 included in Exhibit 99.1 of MPLX LP’s Current Report on Form 8-K dated September 1, 2017 have been incorporated herein in reliance on the report dated February 13, 2015 of KPMG LLP, independent auditors, incorporated by reference herein on the authority of said firm as experts in accounting and auditing.

The audited financial statements of Illinois Extension Pipeline Company, L.L.C. included in Exhibit 99.3 of MPLX LP’s Current Report on Form 8-K dated September 1, 2017 have been incorporated herein in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, on the authority of said firm as experts in auditing and accounting.

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The audited historical financial statements of LOOP LLC as of December 31, 2016 and for the year then ended included in Exhibit 99.5 of MPLX LP’s Current Report on Form 8-K dated September 1, 2017 have been incorporated herein in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, on the authority of said firm as experts in auditing and accounting.

The financial statements of LOOP LLC as of December 31, 2015 and for each of the years in the two-year period ended December 31, 2015 included in Exhibit 99.5 of MPLX LP’s Current Report on Form 8-K dated September 1, 2017 have been incorporated by reference herein in reliance on the report of KPMG LLP, independent accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

The audited historical financial statements of LOCAP LLC as of December 31, 2016 and for the year then ended included in Exhibit 99.7 of MPLX LP’s Current Report on Form 8-K dated September 1, 2017 have been incorporated herein in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, on the authority of said firm as experts in auditing and accounting.

The financial statements of LOCAP LLC as of December 31, 2015 and for each of the years in the two-year period ended December 31, 2015 included in Exhibit 99.7 of MPLX LP’s Current Report on Form 8-K dated September 1, 2017 have been incorporated herein in reliance on the report of KPMG LLP, independent accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

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TABLE OF CONTENTS

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or SEC, using a “shelf” registration process. Using this shelf registration process, we may offer, at any time and from time to time, in one or more offerings, the securities that this prospectus describes. This prospectus provides you with a general description of the securities that we may offer. Each time we use this prospectus to offer securities, we will provide a prospectus supplement that will describe the specific terms of the offering. The prospectus supplement may also add to, update or change the information contained in this prospectus. Please carefully read this prospectus and any prospectus supplement in addition to the information contained in the documents we refer to under the headings “Where You Can Find More Information” and “Information We Incorporate by Reference.”

You should rely only on the information contained or incorporated by reference in this prospectus and in any prospectus supplement or in any free writing prospectus that we may provide you. We have not authorized anyone to provide you with different information. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. You should not assume that the information contained in this prospectus, any prospectus supplement, any document incorporated by reference or any free writing prospectus is accurate as of any date, other than the date mentioned on the cover page of these documents. We are not making offers to sell securities in any jurisdiction in which an offer or solicitation is not authorized or in which the person making such offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make an offer or solicitation.

Except as otherwise indicated, references in this prospectus to “MPLX LP,” “MPLX,” the “Partnership,” “we,” “us” and “our” refer to MPLX LP and its consolidated subsidiaries. References in this prospectus to “Marathon Petroleum Corporation,” “Marathon Petroleum” or “MPC” refer to Marathon Petroleum Corporation and its consolidated subsidiaries other than MPLX.

WHERE YOU CAN FIND MORE INFORMATION

We are subject to the informational reporting requirements of the Securities Exchange Act of 1934, or the Exchange Act. We file annual, quarterly and current reports and other information with the SEC. You can read and copy these materials at the SEC’s public reference room at 100 F Street, N.E., Washington, D.C. 20549. You can obtain information about the operation of the SEC’s public reference room by calling the SEC at 1-800-SEC-0330. The SEC also maintains an Internet site that contains information MPLX has filed electronically with the SEC, which you can access over the Internet at http://www.sec.gov. You can also obtain information about MPLX at our website at http://www.mplx.com. We do not intend for information contained on our website to be part of this prospectus, other than documents that we file with the SEC that are incorporated by reference in this prospectus.

This prospectus is part of a registration statement we have filed with the SEC relating to the securities we may offer. As permitted by SEC rules, this prospectus does not contain all the information we have included in the registration statement and the accompanying exhibits and schedules we have filed with the SEC. You may refer to the registration statement, exhibits and schedules for more information about us and the securities. The registration statement, exhibits and schedules are available at the SEC’s public reference room or through its Internet site.

INFORMATION WE INCORPORATE BY REFERENCE

The SEC allows us to “incorporate by reference” into this prospectus the information in documents we have filed with it, which means that we can disclose important information to you by referring you to those documents. The

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information we incorporate by reference is considered to be a part of this prospectus, and information that we file later with the SEC will automatically update and supersede this information. Any statement contained in any document incorporated or deemed to be incorporated by reference herein shall be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in or omitted from this prospectus or any accompanying prospectus supplement, or in any other subsequently filed document that also is or is deemed to be incorporated by reference herein, modifies or supersedes such statement. Any such statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus. We incorporate by reference the following documents into this prospectus:

We also incorporate by reference any future filings we make with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Exchange Act (excluding information deemed to be furnished and not filed with the SEC) until the termination of this offering. We do not and will not, however, incorporate by reference in this prospectus any documents or portions thereof that are not deemed “filed” with the SEC, including any information furnished pursuant to Item 2.02 or Item 7.01 of our Current Reports on Form 8-K unless, and except to the extent, specified in such current reports.

You may request a copy of these filings, other than an exhibit to these filings unless we have specifically incorporated that exhibit by reference into the filing, at no cost, by writing or telephoning MPLX at the following address:

MPLX LP

200 E. Hardin Street

Findlay, Ohio 45840

Attention: Investor Relations

Telephone: (419) 421-2414

DISCLOSURES REGARDING FORWARD-LOOKING STATEMENTS

This prospectus, including the documents incorporated herein by reference, includes forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, which we refer to as the “Securities Act,” and Section 21E of the Exchange Act. You can identify our forward-looking statements by words such as “anticipate,” “believe,” “design,” “estimate,” “objective,” “expect,” “forecast,” “goal,” “guidance,” “imply,”

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“intend,” “opportunity,” “outlook,” “plan,” “position,” “potential,” “predict,” “project,” “prospective,” “pursue,” “seek,” “strategy,” “target,” “could,” “may,” “should,” “would,” “will” or other similar expressions that convey the uncertainty of future events or outcomes. When considering these forward-looking statements, you should keep in mind the risk factors and other cautionary statements contained in this prospectus and the documents we have incorporated by reference.

Forward-looking statements include, but are not limited to, statements that relate to, or statements that are subject to risks, contingencies or uncertainties that relate to:

We have based our forward-looking statements on our current expectations, estimates and projections about our industry and our partnership. We caution that these statements are not guarantees of future performance, and you should not unduly rely on them, as they involve risks, uncertainties, and assumptions that we cannot predict. In addition, we have based many of these forward-looking statements on assumptions about future events that may prove to be inaccurate. While our management considers these assumptions to be reasonable, they are inherently subject to significant business, economic, competitive, regulatory and other risks, contingencies and uncertainties, most of which are difficult to predict and many of which are beyond our control. Accordingly, our actual results may differ materially from the future performance that we have expressed or forecast in our forward-looking statements. Differences between actual results and any future performance suggested in our forward-looking statements could result from a variety of factors, including the following:

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We undertake no obligation to update the forward-looking statements included or incorporated by reference in this prospectus except to the extent required by applicable law.

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THE COMPANY

We are a diversified, growth-oriented master limited partnership formed in 2012 by Marathon Petroleum to own, operate, develop and acquire midstream energy infrastructure assets. We are engaged in the gathering, processing and transportation of natural gas; the gathering, transportation, fractionation, storage and marketing of NGLs; and the transportation, storage and distribution of crude oil and refined petroleum products. As of June 30, 2017, our assets consisted of a network of crude oil and products pipeline assets located in the Midwest and Gulf Coast regions of the United States; 62 light-product terminals with approximately 24 million barrels of storage capacity; an inland marine business; storage caverns with approximately 2.8 million barrels of storage capacity; crude oil and product storage facilities (tank farms) with approximately 5 million barrels of available storage capacity; a barge dock facility with approximately 78,000 barrels per day of crude oil and product throughput capacity; and gathering and processing assets that include approximately 5.6 billion cubic feet per day of gathering capacity, 7.8 billion cubic feet per day of natural gas processing capacity and 570,000 barrels per day of fractionation capacity.

All of our operations and assets are located in the United States. Our principal executive offices are located at 200 E. Hardin Street, Findlay, Ohio 45840, and our telephone number at that location is (419) 421-2414.

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RISK FACTORS

You should carefully consider any specific risks set forth under the caption “Risk Factors” in the applicable prospectus supplement and under the caption “Risk Factors” included in our most recent Annual Report on Form 10-K filed with the SEC, in each case as these risk factors are amended or supplemented by subsequent Quarterly Reports on Form 10-Q that are incorporated by reference in this prospectus, before making an investment decision. For more information, see “Where You Can Find More Information” and “Information We Incorporate By Reference.” The risks and uncertainties we have described are not the only ones we face. Additional risks and uncertainties that are not yet identified may also materially harm our business, operating results and financial condition and could result in a complete loss of your investment.

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USE OF PROCEEDS

Unless we inform you otherwise in the applicable prospectus supplement, the net proceeds from the sale of securities will be used for general partnership purposes, including repayment or refinancing of debt and funding for acquisitions, working capital requirements and capital expenditures. Pending any specific application, we may initially invest funds in short-term marketable securities or apply them to the reduction of short-term indebtedness.

RATIO OF EARNINGS TO FIXED CHARGES

Our ratios of earnings to fixed charges for each of the periods indicated are as follows:

The term “earnings” is the amount resulting from adding the following items to the extent applicable:

and subtracting from the total the following:

For this purpose, “fixed charges” consists of:

Preference security distributions is the amount of pre-tax earnings that was required to pay distributions on the outstanding Series A Preferred units (as defined below).

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DESCRIPTION OF DEBT SECURITIES

In this summary description of debt securities, references to “MPLX,” “Issuer,” “we,” “our” or “us” mean only MPLX LP and not any of its subsidiaries.

The debt securities that MPLX may offer will be either senior debt securities or subordinated debt securities (including any debt securities that are senior subordinated debt securities). The senior debt securities will be issued under the indenture, dated as of February 12, 2015 (as amended or supplemented to the date hereof), which we refer to in this prospectus as the senior indenture, between us and The Bank of New York Mellon Trust Company, N.A., as trustee. The subordinated debt securities will be issued under a subordinated indenture, which we refer to in this prospectus as the subordinated indenture, to be entered into between us and The Bank of New York Mellon Trust Company, N.A., as trustee. The senior indenture is, and the subordinated indenture will be, subject to, and governed by, the Trust Indenture Act of 1939, as amended. Each of the senior indenture and, after it is executed, the subordinated indenture may be amended, modified or supplemented from time to time. We refer to the senior indenture and the subordinated indenture collectively as the indentures and to each trustee under the indentures as a trustee.

This prospectus summarizes the material provisions of the indentures and what we expect to be the material terms of the debt securities that MPLX may issue under the indentures. This summary is not complete and may not describe all of the provisions of the indentures or of any of the debt securities that might be important to you. For additional information, you should carefully read the senior indenture and the form of subordinated indenture that are incorporated by reference as exhibits to the registration statement of which this prospectus forms a part.

At the time that MPLX offers to sell a particular series of debt securities, we will describe the specific terms of those debt securities in a supplement to this prospectus. We will also indicate in the supplement whether or not the general terms in this prospectus apply to a particular series of debt securities. Accordingly, for a description of the terms of a particular issue of debt securities, you should carefully read both this prospectus and the applicable prospectus supplement.

General

MPLX may issue an unlimited principal amount of debt securities in separate series. The maximum aggregate principal amount for the debt securities of any series may be specified. The debt securities will have terms that are consistent with the indentures. Senior debt securities will be unsecured and unsubordinated obligations of MPLX and will rank equal with all our other unsecured and unsubordinated debt. Subordinated debt securities will be paid only if all payments due under our senior indebtedness, including any outstanding senior debt securities, have been made.

The applicable prospectus supplement for any issuance of debt securities will describe the debt securities and the price or prices at which MPLX will offer the debt securities. The description will include the following:

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The applicable prospectus supplement relating to any debt securities we offer will include a discussion of certain material U.S. federal income tax consequences relating to ownership of the debt securities, including, if applicable, any material U.S. federal income tax consequences applicable to any debt securities issued or deemed to be issued at a discount or applicable to any debt securities that are denominated in a currency or unit other than U.S. dollars.

Conversion and Exchange Rights

The applicable prospectus supplement will describe, if applicable, the terms on which the holders may convert debt securities into or exchange them for common units or other classes of units representing limited partner interests. The conversion or exchange may be mandatory or may be at the holder’s option. The applicable prospectus supplement will describe how the amount of debt securities and number of common units or other classes of units representing limited partner interests to be received upon conversion or exchange would be calculated.

Subordination of Subordinated Debt Securities

The indebtedness underlying any subordinated debt securities will be payable only if all payments due under our senior indebtedness, as defined in the applicable indenture and any indenture supplement, including any outstanding senior debt securities, have been made. If we distribute our assets to creditors upon any liquidation or dissolution or in bankruptcy, reorganization, insolvency, receivership or similar proceedings, we must first pay all amounts due or to become due on all senior indebtedness before we pay the principal of, or premium, if any, or interest on, the subordinated debt securities. In the event the subordinated debt securities are accelerated

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because of an event of default, we may not make any payment on the subordinated debt securities until we have paid all senior indebtedness or the acceleration is rescinded. If the payment of subordinated debt securities accelerates because of an event of default, we must promptly notify holders of senior indebtedness of the acceleration.

If we experience a bankruptcy, dissolution, liquidation, winding-up or reorganization, the holders of senior indebtedness may receive more, ratably, and holders of subordinated debt securities may receive less, ratably, than our other creditors. The indenture for subordinated debt securities may not limit our ability to incur additional senior indebtedness.

Form, Exchange and Transfer

MPLX will issue debt securities only in fully registered form, without coupons, and only in denominations of $1,000 and integral multiples thereof, unless the applicable prospectus supplement provides otherwise. The holder of a debt security may elect, subject to the terms of the indentures and the limitations applicable to global securities, to exchange them for other debt securities of the same series of any authorized denomination and of similar terms and aggregate principal amount.

Holders of debt securities may present them for exchange as provided above or for registration of transfer, duly endorsed or with the form of transfer duly executed, at the office of the registrar we designate for that purpose. We will not impose a service charge for any registration of transfer or exchange of debt securities, but we may require a payment sufficient to cover any tax or other governmental charge payable in connection with the transfer or exchange. We will name the registrar in the applicable prospectus supplement. We may designate additional registrars or rescind the designation of any registrar or approve a change in the office through which any registrar acts, but we must maintain a registrar in each place where we will make payment on debt securities.

If we redeem the debt securities, we will not be required to issue, register the transfer of or exchange any debt security during a specified period prior to mailing a notice of redemption. We are not required to register the transfer of or exchange of any debt security selected for redemption, except the unredeemed portion of the debt security being redeemed.

Global Securities

The debt securities may be represented, in whole or in part, by one or more global securities that will have an aggregate principal amount equal to that of all debt securities of that series. Each global security will be registered in the name of a depositary identified in the applicable prospectus supplement or its nominee. We will deposit the global security with the depositary or a custodian, and the global security will bear a legend regarding the restrictions on exchanges and registration of transfer.

No global security may be exchanged in whole or in part for debt securities registered, and no transfer of a global security in whole or in part may be registered, in the name of any person other than the depositary or any nominee or successor of the depositary unless:

The depositary will determine how all securities issued in exchange for a global security will be registered.

As long as the depositary or its nominee is the registered holder of a global security, we will consider the depositary or the nominee to be the sole owner and holder of the global security and the underlying debt securities. Except as stated above, owners of beneficial interests in a global security will not be entitled to have the global security or any debt security registered in their names, will not receive physical delivery of certificated debt securities and will not

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be considered to be the owners or holders of the global security or underlying debt securities. We will make all payments of principal, premium and interest on a global security to the depositary or its nominee. The laws of some jurisdictions require that some purchasers of securities take physical delivery of such securities in definitive form. These laws may prevent you from transferring your beneficial interests in a global security.

Only institutions that have accounts with the depositary or its nominee and persons that hold beneficial interests through the depositary or its nominee may own beneficial interests in a global security. The depositary will credit, on its book-entry registration and transfer system, the respective principal amounts of debt securities represented by the global security to the accounts of its participants. Ownership of beneficial interests in a global security will be shown only on, and the transfer of those ownership interests will be effected only through, records maintained by the depositary or any such participant.

The policies and procedures of the depositary may govern payments, transfers, exchanges and other matters relating to beneficial interests in a global security. We and the trustee will assume no responsibility or liability for any aspect of the depositary’s or any participant’s records relating to, or for payments made on account of, beneficial interests in a global security.

Payment and Paying Agents

We will pay principal of, and any premium or interest on, a debt security to the person in whose name the debt security is registered at the close of business on the regular record date for such interest.

We will pay principal of, and any premium or interest on, the debt securities at the office of our designated paying agent. Unless the applicable prospectus supplement indicates otherwise, a corporate trust office of the trustee will be the paying agent for the debt securities.

Any other paying agents we designate for the debt securities of a particular series will be named in the applicable prospectus supplement. We may designate additional paying agents, rescind the designation of any paying agent or approve a change in the office through which any paying agent acts, but we must maintain a paying agent in each place of payment for the debt securities.

The paying agent will return to us all money we pay to it for the payment of the principal of, and any premium or interest on, any debt security that remains unclaimed for a specified period. Thereafter, the holder may look only to us for payment, as a general creditor.

Consolidation, Merger and Sale of Assets

Under the terms of the indentures, so long as any securities remain outstanding, we may not consolidate or enter into a share exchange with or merge with or into any other person, in a transaction in which we are not the surviving entity, or sell, convey, transfer or lease our properties and assets substantially as an entirety to any person, unless:

Other Covenants

A series of debt securities may contain additional financial and other covenants applicable to us and our subsidiaries. The applicable prospectus supplement will contain a description of any such covenants that are added to the applicable indenture specifically for the benefit of holders of a particular series.

Events of Default

Each of the following will constitute an event of default under each indenture:

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If an event of default occurs and continues, both the trustee and holders of a specified percentage in aggregate principal amount of the outstanding securities of that series may declare the principal amount of the debt securities of that series to be immediately due and payable. The holders of a majority in aggregate principal amount of the outstanding securities of that series may rescind and annul the acceleration if all events of default, other than the nonpayment of accelerated principal, premium, if any, or interest that has become due solely because of acceleration have been cured or waived.

Except for its duties in case of an event of default, the trustee will not be obligated to exercise any of its rights or powers at the request or direction of any of the holders, unless the holders have offered the trustee indemnity or security satisfactory to it. If the holders provide this indemnification and subject to conditions specified in the applicable indenture, the holders of a majority in aggregate principal amount of the outstanding securities of any series may direct the time, method and place of conducting any proceeding for any remedy available to the trustee or exercising any trust or power conferred on the trustee with respect to the debt securities of that series.

No holder of a debt security of any series may institute any proceeding with respect to the indentures, or for the appointment of a receiver or a trustee, or for any other remedy, unless:

Modification and Waiver

We and the trustee may change an indenture without the consent of any holders with respect to specific matters, including:

In addition, under the indentures, the rights of holders of a series of notes may be changed by us and the trustee with the written consent of the holders of at least a majority in aggregate principal amount of the outstanding

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debt securities of each series that is affected. However, we and the trustee may only make the following changes with the consent of the holder of any outstanding debt securities affected:

The holders of a majority in principal amount of the outstanding debt securities of any series may waive any past default under the indenture with respect to debt securities of that series, except a default in the payment of principal of, or any premium or interest on, any debt security of that series or in respect of a covenant or provision of the indenture that cannot be amended without each holder’s consent.

Except in limited circumstances, we may set any day as a record date for the purpose of determining the holders of outstanding debt securities of any series entitled to give or take any direction, notice, consent, waiver or other action under the indentures. In limited circumstances, the trustee may set a record date. To be effective, the action must be taken by holders of the requisite principal amount of such debt securities computed as of the record date.

Defeasance

To the extent stated in the applicable prospectus supplement, we may elect to apply the provisions in the indentures relating to defeasance and satisfaction and discharge of indebtedness, or to defeasance of restrictive covenants, to the debt securities of any series. The indentures provide that, upon satisfaction of the requirements described below, we may terminate all of our obligations under the debt securities of any series and the applicable indenture, known as legal defeasance, other than our obligation:

In addition, we may terminate our obligation to comply with any restrictive covenants under the debt securities of any series or the applicable indenture, known as covenant defeasance.

We may exercise our legal defeasance option even if we have previously exercised our covenant defeasance option. If we exercise either defeasance option, payment of the notes may not be accelerated because of the occurrence of events of default.

To exercise either defeasance option as to debt securities of any series, we must irrevocably deposit in trust with the trustee money and/or obligations backed by the full faith and credit of the United States that will provide money in an amount sufficient without reinvestment, in the written opinion of a nationally recognized firm of independent public accountants, to pay the principal of, premium, if any, and each installment of interest on the debt securities. We may only establish this trust if, among other things:

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Notices

We will mail notices to holders of debt securities as indicated in the applicable prospectus supplement.

Title

We may treat the person in whose name a debt security is registered as the absolute owner, whether or not such debt security may be overdue, for the purpose of making payment and for all other purposes.

Governing Law

The senior indenture is, and the subordinated indenture, the guarantees and the debt securities will be, governed by and construed in accordance with the laws of the State of New York.

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DESCRIPTION OF THE COMMON UNITS

The common units represent limited partner interests in us. The holders of common units are entitled to participate in partnership distributions and are entitled to exercise the rights and privileges available to limited partners under our Third Amended and Restated Agreement of Limited Partnership, dated as of October 31, 2016 and amended as of February 23, 2017, which we refer to as the Partnership Agreement, filed as an exhibit to the Form S-3 registration statement, of which this prospectus forms a part. For a description of the relative rights and preferences of holders of common units in and to partnership distributions, please read this section and “Provisions of our Partnership Agreement Relating To Cash Distributions.” For a description of the rights and privileges of holders of common units under the Partnership Agreement, including voting rights, please read “Our Partnership Agreement.” We urge you to read the Partnership Agreement, as the Partnership Agreement, and not this description, governs our common units.

Units Outstanding

As of August 30, 2017, we had 388,527,607 common units outstanding, of which 288,947,918 were held by the public and 99,579,689 were held by affiliates of MPC (excluding common units held by officers and directors of our general partner or MPC). As of August 30, 2017, the common units represented an aggregate 98.0% limited partner interest in us and the 7,929,133 general partner units held by our general partner represented a 2.0% general partner interest in us. In addition, as of August 30, 2017, we had 30,769,232 Series A Convertible Preferred units representing limited partner interests in us, which we refer to as the Series A Preferred units, outstanding. The Series A Preferred units are not deemed to represent any percentage interest in the Partnership unless or until they are converted into common units under certain circumstances described in “Description of Other Classes of Units Representing Limited Partner Interests—Series A Preferred Units.” The Series A Preferred units constituted an approximate 7.2% limited partner interest in the Partnership on an as-converted basis and assuming a one-to-one conversion ratio as of August 30, 2017.

Exchange Listing

Our common units are listed on the New York Stock Exchange under the symbol “MPLX.”

Transfer Agent and Registrar

Computershare Trust Company, N.A. serves as the registrar and transfer agent for our common units. We will pay all fees charged by the transfer agent for transfers of common units, except the following that must be paid by our unitholders:

There will be no charge to our unitholders for disbursements of our cash distributions. We will indemnify the transfer agent, its agents and each of their respective stockholders, directors, officers and employees against all claims and losses that may arise out of acts performed or omitted for its activities in that capacity, except for any liability due to any gross negligence or intentional misconduct of the indemnified person or entity.

The transfer agent may resign, by notice to us, or be removed by us. The resignation or removal of the transfer agent will become effective upon our appointment of a successor transfer agent and registrar and its acceptance of the appointment. If no successor has been appointed and has accepted the appointment within 30 days after notice of the resignation or removal, our general partner may act as the transfer agent and registrar until a successor is appointed.

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Transfer of Common Units

By transfer of common units in accordance with the Partnership Agreement, each transferee of common units shall be admitted as a limited partner with respect to the common units transferred when such transfer and admission are reflected in our books and records. Each transferee:

Our general partner will cause any transfers to be recorded on our books and records no less frequently than quarterly.

We may, at our discretion, treat the nominee holder of a common unit as the absolute owner. In that case, the beneficial holder’s rights are limited solely to those that it has against the nominee holder as a result of any agreement between the beneficial owner and the nominee holder.

Common units are securities and transferable according to the laws governing the transfer of securities. In addition to other rights acquired upon transfer, the transferor gives the transferee the right to become a substituted limited partner in our partnership for the transferred common units.

Until a common unit has been transferred on our books, we and the transfer agent may treat the record holder of the common unit as the absolute owner for all purposes, except as otherwise required by law or stock exchange regulations.

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DESCRIPTION OF OTHER CLASSES OF UNITS REPRESENTING LIMITED PARTNER INTERESTS

Our Partnership Agreement authorizes us to issue an unlimited number of limited partner interests and other equity securities in one or more classes, or one or more series of classes with the designations, preferences, rights, powers and duties fixed by our general partner without the approval of any of our limited partners. A copy of our Partnership Agreement is filed as an exhibit to the registration statement of which this prospectus is a part. As of August 30, 2017, we had 30,769,232 Series A Preferred units outstanding, which were held by private investors. The Series A Preferred units are not deemed to represent any percentage interest in the Partnership unless or until they are converted into common units under certain circumstances described below. As of August 30, 2017, on an as-converted basis and assuming a one-to-one conversion ratio, the Series A Preferred units constituted an approximate 7.2% limited partner interest in the Partnership. As of August 30, 2017, no classes of units representing limited partner interests were outstanding other than the common units and the Series A Preferred units.

Series A Preferred Units

The Series A Preferred units rank senior to all other classes or series of limited partner interests of the Partnership with respect to distribution rights and rights upon liquidation. The Series A Preferred units are entitled to receive cumulative quarterly distributions as described under “Provisions of our Partnership Agreement Relating To Cash Distributions—Series A Preferred Unit Distributions.” The Series A Preferred units are entitled to vote on an as-converted basis with the common units, voting together as a single class, on all matters on which the common units are entitled to vote, and have certain other rights to vote as a separate class with respect to any amendment to the Partnership Agreement or the Partnership’s certificate of limited partnership that would be materially adverse to any of the rights, preferences or privileges of the Series A Preferred units and certain other matters.

Each holder of the Series A Preferred units may elect to convert all or any portion of the Series A Preferred units owned by it into common units initially on a one-for-one basis, subject to customary anti-dilution adjustments and an adjustment for any distributions that have accrued but not been paid when due, which we refer to as the Series A conversion rate, at any time (but not more often than once per quarter) after May 13, 2019 (or earlier liquidation, dissolution or winding up of the Partnership), provided that any conversion is for at least $100 million (calculated based on the closing price of the common units on the trading day immediately prior to the notice of conversion) or such lesser amount if such conversion is of all of a holder’s remaining Preferred units.

The Partnership may elect to convert all or any portion of the Series A Preferred units into common units based on the then-applicable Series A conversion rate at any time (but not more often than once per quarter) after May 13, 2020 if (i) the closing price of the common units is greater than 150% of the per unit purchase price for the Series A Preferred units in the private placement described above (or $32.50, as adjusted to reflect splits, combinations or similar events) for the preceding 20 trading days, (ii) the average daily trading volume of the common units is equal to or exceeded one million (as adjusted to reflect splits, combinations or similar events) for the preceding 20 trading days and (iii) the Partnership has an effective registration statement on file covering resales of the common units into which the Series A Preferred units are convertible, provided that the conversion is for at least $100 million (calculated based on the closing trading price of common units on the trading day immediately prior to the notice of conversion) or such lesser amount if such conversion is of all of the then outstanding Series A Preferred units.

In addition, the Series A Preferred units are convertible at certain conversion premiums, either at our election or the election of the holders, upon the occurrence of certain transactions, including certain transactions constituting a change in control of us or an acquisition by MPC or any of its affiliates of all of the outstanding common units or substantially all of our assets.

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The Series A Preferred units are transferable, subject to certain restrictions and the satisfaction of certain conditions on transfer set forth in the Partnership Agreement, in increments of not less than $50 million (based on the per unit purchase price of the Series A Preferred units) or such lessor amount if it constitutes the remaining number of Series A Preferred units owned by such investor.

The Partnership has entered into a Registration Rights Agreement with the purchasers of the Series A Preferred units pursuant to which, among other things, the Partnership has agreed to file and maintain a registration statement with respect to the resale of the Series A Preferred units and the common units that are issuable upon conversion of the Series A Preferred units. If the Partnership fails to cause such registration statement to become effective by a specified date, the Partnership will be required to pay certain amounts to the holders of the Series A Preferred units and any common units issued upon conversion of the Series A Preferred units as liquidated damages. In addition, subject to certain customary limitations and qualifications, the Series A Preferred holders may require the Partnership to initiate underwritten offerings for the common units that are issuable upon conversion of the Series A Preferred units.

Other Classes of Units

If we offer other classes of limited partner interests represented by units other than common units under this prospectus, a prospectus supplement relating to the particular class or series of units offered will include the specific terms of those units, including, among other things, the following:

The applicable prospectus supplement relating to any such units we offer will also include a discussion of certain material U.S. federal income tax consequences relating to ownership of the units (other than those consequences described in this prospectus).

The particular terms of any class or series of units will also be described in the amendment to our Partnership Agreement relating to that class or series of units, which will be filed as an exhibit to or incorporated by reference in this prospectus at or before the time of issuance of any such class or series of units.

The transfer agent, registrar and distributions disbursement agent for the units will be designated in the applicable prospectus supplement.

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PROVISIONS OF OUR PARTNERSHIP AGREEMENT RELATING TO CASH DISTRIBUTIONS

Set forth below is a summary of the significant provisions of the Partnership Agreement that relate to cash distributions.

Distributions of Available Cash

General

The Partnership Agreement requires that, within 60 days after the end of each quarter, we distribute all of our available cash to unitholders of record on the applicable record date.

Definition of Available Cash

Available cash generally means, for any quarter, all cash and cash equivalents on hand at the end of that quarter:

The purpose and effect of the last bullet point above is to allow our general partner, if it so decides, to use cash from working capital borrowings made after the end of the quarter to pay distributions to unitholders. Under the Partnership Agreement, working capital borrowings are generally borrowings that are made under a credit facility, commercial paper facility or similar financing arrangement, and in all cases are used solely for working capital purposes or to pay distributions to partners and with the intent of the borrower to repay such borrowings within 12 months with funds other than from additional working capital borrowings.

Intent to Distribute the Minimum Quarterly Distribution

Under our current cash distribution policy, we intend to make a minimum quarterly distribution to the holders of our common units of $0.2625 per unit, or $1.05 per unit on an annualized basis, to the extent we have sufficient cash from our operations after the establishment of cash reserves and the payment of costs and expenses, including reimbursements of expenses to our general partner. However, there is no guarantee that we will pay the minimum quarterly distribution on our units in any quarter. The amount of distributions paid under our policy and the decision to make any distribution is determined by our general partner, taking into consideration the terms of the Partnership Agreement.

General Partner Interest and Incentive Distribution Rights

Our general partner is entitled to 2.0% of all quarterly distributions that we make prior to our liquidation based on its 2.0% general partner interest in us, which was represented by 7,929,133 general partner units as of

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August 30, 2017. Our general partner has the right, but not the obligation, to contribute a proportionate amount of capital to us to maintain its current general partner interest. The general partner’s 2.0% interest in these distributions will be reduced if we issue additional units in the future and our general partner does not contribute a proportionate amount of capital to us to maintain its 2.0% general partner interest.

Our general partner also currently holds incentive distribution rights that entitle it to receive increasing percentages, up to a maximum of 48.0%, of the cash we distribute from operating surplus (as defined below) in excess of $0.301875 per unit per quarter. The maximum distribution of 48.0% does not include any distributions that our general partner and its affiliates may receive on the common units and general partner units that they own.

Series A Preferred Unit Distributions

The holders of the Series A Preferred units are entitled to receive cumulative quarterly distributions equal to $0.528125 per unit for any quarter ending on or before May 13, 2018, and thereafter the quarterly distributions on each Series A Preferred unit will equal the greater of $0.528125 per unit or the amount that each Series A Preferred unit would have otherwise received if it had been converted into common units at the then-applicable Series A conversion rate. The Partnership may not pay any distributions for any quarter on any junior securities, including any of the common units and the incentive distribution rights, unless the distribution payable to the Series A Preferred units with respect to such quarter, together with any previously accrued and unpaid distributions to the Series A Preferred units, have been paid in full.

Operating Surplus and Capital Surplus

General

All cash distributed to unitholders will be characterized as either being paid from “operating surplus” or “capital surplus.” We treat distributions of available cash from operating surplus differently than distributions of available cash from capital surplus.

Operating Surplus

We define operating surplus as:

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As described above, operating surplus does not reflect actual cash on hand that is available for distribution to our unitholders and is not limited to cash generated by operations. For example, it includes a provision that will enable us, if we choose, to distribute as operating surplus up to $60.0 million of cash we receive in the future from non-operating sources such as asset sales, issuances of securities and long-term borrowings that would otherwise be distributed as capital surplus. In addition, the effect of including, as described above, certain cash distributions on equity interests in operating surplus will be to increase operating surplus by the amount of any such cash distributions. As a result, we may also distribute as operating surplus up to the amount of any such cash that we receive from non-operating sources.

The proceeds of working capital borrowings increase operating surplus and repayments of working capital borrowings are generally operating expenditures (as described below) and thus reduce operating surplus when repayments are made. However, if working capital borrowings, which increase operating surplus, are not repaid during the 12-month period following the borrowing, they will be deemed repaid at the end of such period, thus decreasing operating surplus at such time. When such working capital borrowings are in fact repaid, they will not be treated as a further reduction in operating surplus because operating surplus will have been previously reduced by the deemed repayment.

We define interim capital transactions as (i) borrowings, refinancings or refundings of indebtedness (other than working capital borrowings and items purchased on open account or for a deferred purchase price in the ordinary course of business) and sales of debt securities, (ii) sales of equity securities, and (iii) sales or other dispositions of assets, other than sales or other dispositions of inventory, accounts receivable and other assets in the ordinary course of business and sales or other dispositions of assets as part of normal asset retirements or replacements.

We define operating expenditures as all of our cash expenditures, including, but not limited to, taxes, reimbursements of expenses of our general partner and its affiliates, officer, director and employee compensation, debt service payments, payments made in the ordinary course of business under interest rate hedge contracts and commodity hedge contracts (provided that payments made in connection with the termination of any interest rate hedge contract or commodity hedge contract prior to the expiration of its settlement or termination date specified therein will be included in operating expenditures in equal quarterly installments over the remaining scheduled life of such interest rate hedge contract or commodity hedge contract and amounts paid in connection with the initial purchase of a rate hedge contract or a commodity hedge contract will be amortized at the life of such rate hedge contract or commodity hedge contract), maintenance capital expenditures (as discussed in further detail below), and repayment of working capital borrowings; provided, however, that operating expenditures do not include:

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Capital Surplus

Capital surplus is defined in the Partnership Agreement as any distribution of available cash in excess of our cumulative operating surplus. Accordingly, except as described above, capital surplus would generally be generated by:

Characterization of Cash Distributions

All available cash distributed by us on any date from any source will be treated as distributed from operating surplus until the sum of all available cash distributed by us since October 31, 2012, the closing of our Initial Public Offering, equals the operating surplus from such date through the end of the quarter immediately preceding that distribution. We anticipate that distributions from operating surplus will generally not represent a return of capital. However, operating surplus, as defined in the Partnership Agreement, includes certain components, including a $60.0 million cash basket, that represent non-operating sources of cash. Consequently, it is possible that all or a portion of specific distributions from operating surplus may represent a return of capital. Any available cash distributed by us in excess of our cumulative operating surplus will be deemed to be capital surplus under the Partnership Agreement. The Partnership Agreement treats a distribution of capital surplus as the repayment of the initial unit price from our Initial Public Offering and as a return of capital. We do not anticipate that we will make any distributions from capital surplus.

Capital Expenditures

Maintenance capital expenditures are cash expenditures (including expenditures for the construction or development of new capital assets or the replacement, improvement or expansion of existing capital assets) made to maintain, over the long term, our operating capacity or operating income. Examples of maintenance capital expenditures are expenditures to repair, refurbish and replace pipelines and storage facilities, to maintain equipment reliability, integrity and safety and to address environmental laws and regulations.

Expansion capital expenditures are cash expenditures incurred for acquisitions or capital improvements that we expect will increase our operating capacity or operating income over the long term. Examples of expansion capital expenditures include the acquisition of equipment, or the construction, development or acquisition of additional pipeline or storage capacity to the extent such capital expenditures are expected to expand our long-term operating capacity or operating income. Expansion capital expenditures include interest payments (and related fees) on debt incurred to finance all or a portion of expansion capital expenditures in respect of the period from the date that we enter into a binding obligation to commence the construction, development, replacement, improvement or expansion of a capital asset and ending on the earlier to occur of the date that such capital improvement commences commercial service and the date that such capital improvement is abandoned or disposed of. Capital expenditures that are made in part for maintenance capital purposes and in part for expansion capital purposes will be allocated as maintenance capital expenditures or expansion capital expenditures by our general partner.

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Adjusted Operating Surplus

Adjusted operating surplus is intended to reflect the cash generated from operations during a particular period and therefore excludes net drawdowns of reserves of cash established in prior periods. Adjusted operating surplus for a period consists of:

Distributions of Available Cash from Operating Surplus

After payment of the cumulative quarterly distributions on the Series A Preferred units, we will make distributions of available cash from operating surplus for any quarter in the following manner:

The preceding discussion is based on the assumptions that our general partner maintains its 2.0% general partner interest and that we do not issue additional classes of equity securities.

General Partnership Interest and Incentive Distribution Rights

The Partnership Agreement provides that our general partner is entitled to a percentage of all distributions that we make prior to our liquidation equal to its general partner interest in us, which was 2.0% as of August 30, 2017. Our general partner has the right, but not the obligation, to contribute a proportionate amount of capital to us in order to maintain its 2.0% general partner interest if we issue additional units. Our general partner’s 2.0% interest, and the percentage of our cash distributions to which it is entitled from such 2.0% interest, will be proportionately reduced if we issue additional units in the future (other than the issuance of common units upon a reset of the incentive distribution rights) and our general partner does not contribute a proportionate amount of capital to us in order to maintain its 2.0% general partner interest. The Partnership Agreement does not require that our general partner fund its capital contribution with cash. Our general partner may instead fund its capital contribution by the contribution to us of common units or other property.

Incentive distribution rights represent the right to receive an increasing percentage (13.0%, 23.0% and 48.0%) of quarterly distributions of available cash from operating surplus after the minimum quarterly distribution and the target distribution levels have been achieved. Our general partner currently holds the incentive distribution rights, but may transfer these rights separately from its general partner interest, subject to restrictions in the Partnership Agreement.

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The following discussion assumes that our general partner maintains its 2.0% general partner interest, that our general partner continues to own the incentive distribution rights and that we do not issue additional classes of equity securities.

If for any quarter we have paid the cumulative quarterly distributions on the Series A Preferred units and distributed available cash from operating surplus to the common unitholders in an amount equal to the minimum quarterly distribution, then, we will distribute any additional available cash from operating surplus for that quarter among the unitholders and our general partner in the following manner:

Percentage Allocations of Available Cash from Operating Surplus

The following table illustrates the percentage allocations of available cash from operating surplus between the unitholders and our general partner based on the specified target distribution levels. The amounts set forth under “Marginal percentage interest in distributions” are the percentage interests of our general partner and the unitholders in any available cash from operating surplus we distribute per outstanding common unit to common unitholders up to and including the corresponding amount in the column “Total quarterly distribution per unit target amount.” The percentage interests shown for our unitholders and our general partner for the minimum quarterly distribution are also applicable to quarterly distribution amounts that are less than the minimum quarterly distribution. The percentage interests set forth below for our general partner include its 2.0% general partner interest and assume that our general partner has contributed any additional capital necessary to maintain its 2.0% general partner interest, that we have not issued any new classes of partnership interests, our general partner has not transferred its incentive distribution rights and that the cumulative distributions on the Series A Preferred units have been paid in full.

General Partner’s Right to Reset Incentive Distribution Levels

Our general partner, as the initial holder of our incentive distribution rights, has the right under the Partnership Agreement, subject to certain conditions, to elect to relinquish the right to receive incentive distribution payments based on the initial target distribution levels and to reset, at higher levels, the minimum quarterly distribution amount and target distribution levels upon which the incentive distribution payments to our general partner would be set. If our general partner transfers all or a portion of the incentive distribution rights in the future, then the holder or holders of a majority of our incentive distribution rights will be entitled to exercise this

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right. The following discussion assumes that our general partner holds all of the incentive distribution rights at the time that a reset election is made. Our general partner’s right to reset the minimum quarterly distribution amount and the target distribution levels upon which the incentive distributions payable to our general partner are based may be exercised, without approval of our unitholders or the conflicts committee, at any time we have made cash distributions to the holders of the incentive distribution rights at the highest level of incentive distribution for each of the four consecutive fiscal quarters immediately preceding such time and the amount of each such distribution did not exceed adjusted operating surplus for such quarter, respectively. If our general partner and its affiliates are not the holders of a majority of the incentive distribution rights at the time an election is made to reset the minimum quarterly distribution amount and the target distribution levels, then the proposed reset will be subject to the prior written concurrence of the general partner that the conditions described above have been satisfied. The reset minimum quarterly distribution (as defined below) amount and target distribution levels will be higher than the minimum quarterly distribution amount and the target distribution levels prior to the reset such that our general partner will not receive any incentive distributions under the reset target distribution levels until cash distributions per unit following this event increase as described below. We anticipate that our general partner would exercise this reset right in order to facilitate acquisitions or internal growth projects that would otherwise not be sufficiently accretive to cash distributions per common unit, taking into account the existing levels of incentive distribution payments being made to our general partner.

In connection with the resetting of the minimum quarterly distribution amount and the target distribution levels and the corresponding relinquishment by our general partner of incentive distribution payments based on the target distributions prior to the reset, our general partner will be entitled to receive a number of newly issued common units based on a predetermined formula described below that takes into account the “cash parity” value of the average cash distributions related to the incentive distribution rights received by our general partner for the two quarters immediately preceding the reset event as compared to the average cash distributions per common unit during that two-quarter period. In addition, our general partner will be issued the number of general partner units necessary to maintain our general partner’s interest in us immediately prior to the reset election.

The number of common units that our general partner would be entitled to receive from us in connection with a resetting of the minimum quarterly distribution amount and the target distribution levels then in effect would be equal to the quotient determined by dividing (x) the average aggregate amount of cash distributions received by our general partner in respect of its incentive distribution rights during the two consecutive fiscal quarters ended immediately prior to the date of such reset election by (y) the average of the aggregate amount of cash distributed per common unit during each of these two quarters.

Following a reset election, the minimum quarterly distribution amount will be reset to an amount equal to the average cash distribution amount per common unit for the two fiscal quarters immediately preceding the reset election, which amount we refer to as the reset minimum quarterly distribution, and the target distribution levels will be reset to be correspondingly higher such that, after paying the cumulative quarterly distributions on the Series A Preferred units, we would distribute all of our available cash from operating surplus for each quarter thereafter as follows:

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The preceding discussion is based on the assumption that our general partner maintains its 2.0% general partner interest, that we do not issue any new classes of partnership interest and that our general partner has not transferred its incentive distribution rights.

The following table illustrates the percentage allocations of available cash from operating surplus between the unitholders and our general partner at various cash distribution levels (i) pursuant to the cash distribution provisions of the Partnership Agreement and (ii) following a hypothetical reset of the minimum quarterly distribution and target distribution levels. The table assumes that the average quarterly cash distribution amount per common unit during the two fiscal quarters immediately preceding the reset election was $0.50, our general partner’s 2.0% interest has been maintained, we had not issued any new classes of partnership interests and our general partner has not transferred its incentive distribution rights.

The following table illustrates the total amount of available cash from operating surplus, after paying the cumulative quarterly distributions on Series A Preferred units, that would be distributed to the unitholders and our general partner, including in respect of incentive distribution rights, based on an average of the amounts distributed for the two quarters immediately prior to the reset. The table assumes that immediately prior to the reset there would be 332,000,000 common units outstanding, our general partner’s 2.0% interest has been maintained, the average distribution to each common unit would be $0.50 per quarter for the two consecutive non-overlapping quarters prior to the reset, we had not issued any new classes of partnership interests and our general partner has not transferred its incentive distribution rights. The table does not reflect cash distributions paid on any common units acquired by the general partner or any of its affiliates prior to the reset.