As filed with the Securities and Exchange Commission on July 5, 2018

Registration No. 333-225244

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Amendment No. 1

to

FORM S-4

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

MARATHON PETROLEUM CORPORATION

(Exact Name of Registrant as Specified in Its Charter)

539 South Main Street

Findlay, Ohio 45840

Telephone: (419) 422-2121

(Address, including Zip Code, and Telephone Number, Including Area Code, of Registrant’s Principal Executive Offices)

Molly R. Benson

Vice President, Chief Securities, Governance and Compliance Officer and Corporate Secretary

Marathon Petroleum Corporation

539 South Main Street

Findlay, Ohio 45840

(419) 422-2121

(Name, Address, including Zip Code, and Telephone Number, including Area Code, of Agent for Service)

With a copy to:

Approximate date of commencement of proposed sale of the securities to the public: As soon as practicable after this registration statement is declared effective.

If the securities being registered on this form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, please check the following box.  ☐

If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act of 1933, as amended (the “Securities Act”), check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

If this form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act. (Check one):

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.  ☐

If applicable, place an X in the box to designate the appropriate rule provision relied upon in conducting this transaction:

Exchange Act Rule 13c-4(i) (Cross-Border Issuer Tender Offer)  ☐

Exchange Act Rule 14d-1(d) (Cross-Border Third-Party Tender Offer)  ☐

CALCULATION OF REGISTRATION FEE

The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the SEC, acting pursuant to said section 8(a), may determine.

The information in the joint proxy statement/prospectus is not complete and may be changed. These securities may not be issued until the registration statement filed with the Securities and Exchange Commission is effective. The joint proxy statement/prospectus is not an offer to sell these securities and does not constitute the solicitation of offers to buy these securities in any jurisdiction where the offer or sale is not permitted.

PRELIMINARY—SUBJECT TO COMPLETION, DATED JULY 5, 2018

JOINT LETTER TO STOCKHOLDERS OF MARATHON PETROLEUM CORPORATION AND STOCKHOLDERS OF ANDEAVOR

Dear Stockholders:

Marathon Petroleum Corporation, which is referred to as MPC, Andeavor, Mahi Inc. and Mahi LLC have entered into a merger agreement providing for the acquisition of Andeavor by MPC. MPC stockholders as of the close of business on [            ], 2018, the record date, are invited to attend a special meeting of MPC stockholders on [            ], 2018, at [            ] Eastern Time to consider and vote upon a proposal to approve the issuance of MPC common stock in connection with the merger and certain other matters related to the merger, as well as a proposal to increase the number of authorized shares of MPC common stock and a proposal to increase the maximum number of directors permitted to serve on the MPC board. Andeavor stockholders as of the close of business on the record date are invited to attend a special meeting of Andeavor stockholders on [            ], 2018, at [            ] Central Time to consider and vote upon a proposal to adopt the merger agreement and certain other matters related to the merger.

If you are an Andeavor stockholder and the merger contemplated by the merger agreement is completed, you will be entitled to elect to receive, for each issued and outstanding share of Andeavor common stock owned by you immediately prior to the effective time of the merger of Mahi Inc. with and into Andeavor, which is referred to as the first merger, either 1.87 shares of MPC common stock, which is referred to as the stock consideration, or $152.27 in cash, which is referred to as the cash consideration. Elections to receive cash consideration and stock consideration are subject to allocation and proration procedures set forth in the merger agreement to ensure that the total number of shares of Andeavor common stock converted into the right to receive cash consideration is equal to 22,885,359 shares, which is referred to as the cash election number, and the remaining shares of Andeavor common stock to be converted in the merger will be converted into the right to receive stock consideration. If you make no election or an untimely election, or are otherwise deemed not to have submitted an effective form of election, you will be deemed to have made an election to receive the stock consideration. The precise consideration that you will receive will not be known at the time that you vote on the adoption of the merger agreement or make an election because it is dependent upon the aggregate number of shares of Andeavor common stock in respect of which elections to receive the cash consideration and the stock consideration are made. For a description of the consideration that Andeavor stockholders will receive upon completion of the merger, and the potential adjustments to this consideration, see the section entitled “The Merger—Consideration to Andeavor Stockholders” beginning on page 78 of the accompanying joint proxy statement/prospectus.

The market value of the stock consideration, but not the cash consideration, will fluctuate with the price of MPC common stock. Based on the closing price of MPC common stock on April 27, 2018, the last trading day before the public announcement of the signing of the merger agreement, the value of the stock consideration payable to holders of Andeavor common stock upon completion of the merger was approximately $152.27 per share. Based on the closing price of MPC common stock on June 29, 2018, the last practicable date before the date of filing of the joint proxy statement/prospectus accompanying this letter, the value of the stock consideration payable to holders of Andeavor common stock upon completion of the merger was approximately $131.20 per share. Andeavor stockholders should obtain current stock price quotations for MPC common stock and Andeavor common stock. MPC common stock is traded on the New York Stock Exchange, which is referred to as the NYSE, under the symbol “MPC,” and Andeavor common stock is traded on the NYSE under the symbol “ANDV.”

The merger is intended to qualify as a “reorganization” within the meaning of Section 368(a) of the Internal Revenue Code of 1986, as amended, which is referred to as the Internal Revenue Code. Assuming the merger qualifies as a reorganization, a stockholder of Andeavor generally will not recognize any gain or loss upon receipt of the stock consideration in the merger, will recognize gain (but not loss) in an amount not to exceed any cash consideration received in the merger (other than cash received in lieu of a fractional share) and will recognize gain or loss with respect to any cash received in lieu of a fractional share of MPC common stock, as discussed in the section entitled “Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 186 of the accompanying joint proxy statement/prospectus.

MPC and Andeavor will each hold a special meeting of its stockholders to consider certain matters relating to the proposed merger, as well as certain other matters. MPC and Andeavor cannot complete the proposed merger unless, among other things, MPC stockholders approve the issuance of shares of MPC common stock in connection with the merger, and Andeavor stockholders adopt the merger agreement.

Your vote is very important. To ensure your representation at your company’s special meeting, please complete and return the enclosed proxy card or submit your proxy via the Internet or by telephone. Please vote promptly whether or not you expect to attend your company’s special meeting. Submitting a proxy now will not prevent you from being able to vote in person at your company’s special meeting if you are otherwise eligible to vote at such meeting.

Paul L. Foster and Franklin Mountain Investments, LP entered into a voting agreement with MPC, Mahi Inc., Mahi LLC and Andeavor pursuant to which they have agreed, among other things, to vote all of the shares of Andeavor common stock beneficially owned by them (constituting approximately 5.2% of the issued and outstanding shares of Andeavor common stock as of April 26, 2018), excluding certain shares of Andeavor common stock that are subject to a pre-existing 10b5-1 trading plan, in favor of the adoption of the merger agreement and other items, on the terms and subject to the conditions set forth in the voting agreement.

The MPC board of directors has determined that the merger agreement, the voting agreement, the merger and the other transactions contemplated by the merger agreement and the voting agreement are fair to, and in the best interests of, MPC and its stockholders; has unanimously approved the merger agreement, the voting agreement, the merger and the other transactions contemplated by the merger agreement and the voting agreement, including the issuance of shares of MPC common stock in connection with the merger; and unanimously recommends that MPC stockholders vote “FOR” the issuance of MPC common stock in connection with the merger and “FOR” each of the other MPC proposals described in the accompanying joint proxy statement/prospectus.

The Andeavor board of directors has determined that the merger and the other transactions contemplated by the merger agreement are fair to, and in the best interests of, Andeavor and its stockholders; has unanimously approved and declared advisable the merger agreement and the transactions contemplated thereby, including the merger; and unanimously recommends that Andeavor stockholders vote “FOR” the adoption of the merger agreement and the approval of the transactions contemplated thereby, including the merger and “FOR” each of the other Andeavor proposals described in the accompanying joint proxy statement/prospectus.

The obligations of MPC and Andeavor to complete the merger are subject to the satisfaction or waiver of the conditions set forth in the merger agreement, a copy of which is included as part of the accompanying joint proxy statement/prospectus. The joint proxy statement/prospectus provides you with detailed information about the proposed merger. It also contains or references information about MPC and Andeavor and certain related matters. You are encouraged to read the joint proxy statement/prospectus carefully and in its entirety. In particular, you should carefully read the section entitled “Risk Factors” beginning on page 49 of the accompanying joint proxy statement/prospectus for a discussion of risks you should consider in evaluating the proposed merger and the issuance of shares of MPC common stock in connection with the merger and how they will affect you.

Sincerely,

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the merger, the adoption of the merger agreement, the issuance of MPC common stock in connection with the merger, the proposed amendments to the MPC certificate of incorporation or any other transactions described in the accompanying joint proxy statement/prospectus, or passed upon the adequacy or accuracy of the disclosure in this document. Any representation to the contrary is a criminal offense.

This document is dated [            ], 2018, and is first being mailed to stockholders of MPC and Andeavor on or about [            ], 2018.

MARATHON PETROLEUM CORPORATION NOTICE OF SPECIAL MEETING OF STOCKHOLDERS TO BE HELD ON [    ], 2018 IN THE AUDITORIUM OF MARATHON PETROLEUM CORPORATION, 539 SOUTH MAIN STREET, FINDLAY, OHIO 45840

NOTICE IS HEREBY GIVEN that a special meeting of stockholders of Marathon Petroleum Corporation, which is referred to as MPC, will be held on [            ], 2018, at [            ] Eastern Time in the Auditorium of Marathon Petroleum Corporation, 539 South Main Street, Findlay, Ohio 45840, for the following purposes:

MPC stockholder approval of the MPC issuance proposal is required to complete the merger. MPC stockholders will also be asked to approve the MPC authorized stock COI amendment proposal, the MPC board size COI amendment proposal and, if necessary, the MPC adjournment proposal. MPC will transact no other business at the MPC special meeting. The record date for the MPC special meeting has been set as [            ], 2018. Only MPC stockholders of record as of the close of business on such record date are entitled to notice of, and to vote at, the MPC special meeting or any adjournments and postponements thereof. See the section entitled “Special Meeting of MPC Stockholders” beginning on page 63 of the joint proxy statement/prospectus accompanying this notice for additional information.

The MPC board unanimously recommends that you vote “FOR” the MPC issuance proposal, “FOR” the MPC authorized stock COI amendment proposal, “FOR” the MPC board size COI amendment proposal and “FOR” the MPC adjournment proposal.

The MPC stockholder proposals are described in more detail in the accompanying joint proxy statement/prospectus, which you should read carefully in its entirety before you vote. A copy of the merger agreement is attached as Annex A to the accompanying joint proxy statement/prospectus, a copy of the voting agreement is attached as Annex B to the accompanying joint proxy statement/prospectus, a copy of the proposed amendment with respect to the MPC authorized stock COI amendment proposal is attached as Annex F to the accompanying joint proxy statement/prospectus and a copy of the proposed amendment with respect to the MPC board size COI amendment proposal is attached as Annex G to the accompanying joint proxy statement/prospectus.

PLEASE VOTE AS PROMPTLY AS POSSIBLE, WHETHER OR NOT YOU PLAN TO ATTEND THE MPC SPECIAL MEETING. IF YOU LATER DESIRE TO REVOKE OR CHANGE YOUR PROXY FOR ANY REASON, YOU MAY DO SO IN THE MANNER DESCRIBED IN THE ACCOMPANYING JOINT PROXY STATEMENT/PROSPECTUS. FOR FURTHER INFORMATION CONCERNING THE PROPOSALS BEING VOTED UPON, USE OF THE PROXY AND OTHER RELATED MATTERS, YOU ARE URGED TO READ THE ACCOMPANYING JOINT PROXY STATEMENT/PROSPECTUS.

ANDEAVOR

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS

TO BE HELD ON [            ], 2018

AT 19100 RIDGEWOOD PARKWAY

SAN ANTONIO, TX 78259

NOTICE IS HEREBY GIVEN that a special meeting of stockholders of Andeavor will be held on [            ], 2018 at [            ] Central Time at 19100 Ridgewood Parkway, San Antonio, Texas 78259, for the following purposes:

Andeavor stockholder approval of the Andeavor merger proposal is required to complete the merger. Andeavor stockholders will also be asked to approve the Andeavor compensation proposal and, if necessary, the Andeavor adjournment proposal. Andeavor will transact no other business at the Andeavor special meeting. The record date for the Andeavor special meeting has been set as [            ], 2018. Only Andeavor stockholders of record as of the close of business on such record date are entitled to notice of, and to vote at, the Andeavor special meeting or any adjournments and postponements thereof. For additional information, see the section entitled “Special Meeting of Andeavor Stockholders” beginning on page 71 of the joint proxy statement/prospectus accompanying this notice.

The Andeavor board unanimously recommends that you vote “FOR” the Andeavor merger proposal, “FOR” the Andeavor compensation proposal and “FOR” the Andeavor adjournment proposal.

The Andeavor stockholder proposals are described in more detail in the accompanying joint proxy statement/prospectus, which you should read carefully in its entirety before you vote. A copy of the merger agreement is attached as Annex A to the accompanying joint proxy statement/prospectus and a copy of the voting agreement is attached as Annex B to the accompanying joint proxy statement/prospectus.

PLEASE VOTE AS PROMPTLY AS POSSIBLE, WHETHER OR NOT YOU PLAN TO ATTEND THE ANDEAVOR SPECIAL MEETING. IF YOU LATER DESIRE TO REVOKE OR CHANGE YOUR PROXY FOR ANY REASON, YOU MAY DO SO IN THE MANNER DESCRIBED IN THE ACCOMPANYING JOINT PROXY STATEMENT/PROSPECTUS. FOR FURTHER INFORMATION CONCERNING THE PROPOSALS BEING VOTED UPON, USE OF THE PROXY AND OTHER RELATED MATTERS, YOU ARE URGED TO READ THE ACCOMPANYING JOINT PROXY STATEMENT/PROSPECTUS.

REFERENCES TO ADDITIONAL INFORMATION

This joint proxy statement/prospectus incorporates important business and financial information about Marathon Petroleum Corporation, which is referred to as MPC, and Andeavor from other documents that MPC and Andeavor have filed with the Securities and Exchange Commission, which is referred to as the SEC, and that are not contained herein or delivered herewith. For a listing of documents incorporated by reference herein, please see the section entitled “Where You Can Find More Information” beginning on page 234. This information is available for you to review free of charge at the SEC’s public reference room located at 100 F Street, N.E., Washington, DC 20549, and through the SEC’s website at http://www.sec.gov.

You may request copies of this joint proxy statement/prospectus and any of the documents incorporated by reference herein or other information concerning MPC or Andeavor, without charge, upon written or oral request to the applicable company’s principal executive offices. The respective addresses and telephone numbers of such principal executive offices are listed below.

To obtain timely delivery of these documents before MPC’s special meeting of stockholders, MPC stockholders must request the information no later than [            ], 2018, which is five business days before the MPC special meeting.

To obtain timely delivery of these documents before Andeavor’s special meeting of stockholders, Andeavor stockholders must request the information no later than [            ], 2018, which is five business days before the Andeavor special meeting.

In addition, if you have questions about the merger or the accompanying joint proxy statement/prospectus, would like additional copies of the joint proxy statement/prospectus or need to obtain proxy cards or other information related to the proxy solicitation, please contact Innisfree M&A Incorporated, the proxy solicitor for both MPC and Andeavor, toll-free at 1-888-750-5834 or collect at 1-212-750-5833. You will not be charged for any of these documents that you request.

ABOUT THIS JOINT PROXY STATEMENT/PROSPECTUS

This document, which forms part of a registration statement on Form S-4 filed with the SEC by MPC (Registration No. 333-225244), constitutes a prospectus of MPC under Section 5 of the Securities Act of 1933, as amended, which is referred to as the Securities Act, with respect to the shares of common stock of MPC, par value $0.01 per share, which is referred to as MPC common stock, to be issued to Andeavor stockholders pursuant to the Agreement and Plan of Merger, dated as of April 29, 2018, as such agreement may be amended from time to time, which is referred to as the merger agreement, among Andeavor, MPC, Mahi Inc., which is referred to as Merger Sub 1, and Mahi LLC, which is referred to as Merger Sub 2. This document also constitutes a proxy statement of each of MPC and Andeavor under Section 14(a) of the Securities Exchange Act of 1934, as amended, which is referred to as the Exchange Act.

MPC has supplied all information contained or incorporated by reference herein relating to MPC, Merger Sub 1 and Merger Sub 2, and Andeavor has supplied all information contained or incorporated by reference herein relating to Andeavor. MPC and Andeavor have both contributed to the information relating to the merger contained in this joint proxy statement/prospectus.

You should rely only on the information contained in or incorporated by reference herein in connection with any vote, the giving or withholding of any proxy, or any investment decision in connection with the merger. MPC and Andeavor have not authorized anyone to provide you with information that is different from that contained in or incorporated by reference herein. This joint proxy statement/prospectus is dated [            ], 2018, and you should not assume that the information contained in this joint proxy statement/prospectus is accurate as of any date other than such date unless otherwise specifically provided herein. Further, you should not assume that the information incorporated by reference herein is accurate as of any date other than the date of the incorporated document. Neither the mailing of this joint proxy statement/prospectus to MPC or Andeavor stockholders nor the issuance by MPC of shares of its common stock pursuant to the merger agreement will create any implication to the contrary.

TABLE OF CONTENTS

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TABLE OF CONTENTS

(continued)

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TABLE OF CONTENTS

(continued)

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QUESTIONS AND ANSWERS ABOUT THE MERGER AND THE SPECIAL MEETINGS

The following are answers to certain questions that you may have regarding the merger and the MPC and Andeavor special meetings. MPC and Andeavor urge you to read carefully the remainder of this document because the information in this section may not provide all the information that might be important to you in determining how to vote. Additional important information is also contained in the annexes to, and the documents incorporated by reference in, this document.

MPC. The issuance of MPC common stock in connection with the first merger must be approved by the stockholders of MPC in accordance with the rules of the New York Stock Exchange, which are referred to as the NYSE rules, in order for the merger to be consummated. MPC is holding a special meeting of its stockholders, which is referred to as the MPC special meeting, to obtain that approval. MPC stockholders will also be asked to vote on the MPC authorized stock COI amendment proposal and the MPC board size COI amendment proposal, each as defined below, at the MPC special meeting and to approve the adjournment of the MPC special meeting, if necessary or appropriate, to solicit additional proxies in the event there are not sufficient votes at the time of the MPC special meeting to approve the issuance of MPC common stock in connection with the merger.

Andeavor. The merger agreement must be adopted by the stockholders of Andeavor in accordance with the General Corporation Law of the State of Delaware, which is referred to as the DGCL, in order for the merger to be consummated. Andeavor is holding a special meeting of its stockholders, which is referred to as the Andeavor special meeting, to obtain that approval. Andeavor stockholders will also be asked to vote on the Andeavor compensation proposal, as defined below, at the Andeavor special meeting and to approve the adjournment of the Andeavor special meeting, if necessary or appropriate, to solicit additional proxies in the event there are not sufficient votes at the time of the Andeavor special meeting to adopt the merger agreement.

Andeavor. The Andeavor special meeting will be held at [        ] Central Time on [                ], 2018, at 19100 Ridgewood Parkway, San Antonio, Texas 78259.

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Andeavor. The stockholders of Andeavor will be asked to:

Andeavor. Yes. The merger cannot be completed unless the merger agreement is adopted by the holders representing a majority of the outstanding shares of Andeavor common stock entitled to vote thereon at the Andeavor special meeting. Only Andeavor stockholders as of the close of business on the record date are entitled to vote at the Andeavor special meeting. The board of directors of Andeavor, which is referred to as the Andeavor board, unanimously recommends that such Andeavor stockholders vote “FOR” the approval of the Andeavor merger proposal, “FOR” the approval of the Andeavor compensation proposal and “FOR” the approval of the Andeavor adjournment proposal.

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The MPC authorized stock COI amendment proposal. Approval of the MPC authorized stock COI amendment proposal requires the affirmative vote of a majority of the shares of MPC common stock outstanding as of the close of business on the record date and entitled to vote on the proposal. Abstentions will have the same effect as a vote “AGAINST” the proposal.

The MPC board size COI amendment proposal. Approval of the MPC board size COI amendment proposal requires the affirmative vote of at least 80% of the shares of MPC common stock outstanding as of the close of business on the record date and entitled to vote on the proposal. Abstentions will have the same effect as a vote “AGAINST” the proposal.

The MPC adjournment proposal. Approval of the MPC adjournment proposal requires the affirmative vote of a majority of shares held by MPC stockholders present in person or by proxy at the MPC special meeting and entitled to vote on the proposal, regardless of whether a quorum is present. Abstentions will have the same effect as a vote “AGAINST” the proposal.

The Andeavor compensation proposal. Approval of the Andeavor compensation proposal requires the affirmative vote of a majority of the shares of Andeavor common stock present in person or by proxy at the Andeavor special meeting and entitled to vote on the proposal. Abstentions will have the same effect as a vote “AGAINST” the proposal.

The Andeavor adjournment proposal. Approval of the Andeavor adjournment proposal requires the affirmative vote of a majority of the shares of Andeavor common stock present in person or by proxy at the Andeavor special meeting and entitled to vote on the proposal, regardless of whether a quorum is present. Abstentions will have the same effect as a vote “AGAINST” the proposal.

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Elections to receive stock consideration, which are referred to as stock elections, and elections to receive cash consideration, which are referred to as cash elections, are subject to the allocation and proration procedures set forth in the merger agreement to ensure that the total number of shares of Andeavor common stock converted into cash consideration is equal to 22,885,359 shares of Andeavor common stock, which is referred to as the cash election number, and the remaining shares of Andeavor common stock to be converted in the merger will be converted into the right to receive stock consideration.

If you elect to receive stock consideration or are deemed to have elected to receive stock consideration and would otherwise be entitled to receive a fractional share of MPC common stock (taking into account all Andeavor shares for which you have elected or been deemed to have elected to receive stock consideration), you will receive cash in lieu of such fractional share, and you will not be entitled to dividends, voting rights or any other rights in respect of such fractional share. For more information regarding allocation and proration procedures, see the section entitled “The Merger Agreement—Merger Consideration” beginning on page 153.

For more information regarding the stock consideration or cash consideration, as applicable, to be provided to Andeavor stockholders, referred to as the per share merger consideration, see the section entitled “The Merger—Consideration to Andeavor Stockholders” beginning on page 78. For more information regarding election mechanics, see the section entitled “The Merger Agreement—Election and Exchange Procedures” beginning on page 156.

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For example, and by way of illustration only, if the aggregate number of shares of Andeavor common stock with respect to which cash elections are made are three times the cash election number, each record holder of shares of Andeavor common stock will receive cash consideration for approximately one-third of the shares of Andeavor common stock with respect to which such record holder makes a cash election and stock consideration for approximately two-thirds of such shares. For the avoidance of doubt, each record holder making cash elections will, to the extent reasonably possible, receive cash consideration and stock consideration in the same proportion as each other record holder receives in respect of shares of Andeavor common stock with respect to which cash elections have been made.

The calculations described above will be performed by Computershare Trust Company, N.A., which is referred to as the exchange agent.

For the avoidance of doubt, each record holder making stock elections will, to the extent reasonably possible, receive stock consideration and cash consideration in the same proportion as each other record holder receives in respect of shares of Andeavor common stock with respect to which stock elections have been made.

The calculations described above will be performed by the exchange agent.

Treatment of Andeavor Options

At the effective time of the first merger, each outstanding option award to purchase Andeavor common stock, which is referred to as an Andeavor option, whether vested or unvested, will automatically and without any action on the part of the holder thereof, cease to represent an option award to purchase Andeavor common stock and will be converted into an option award to acquire a number of shares of MPC common stock (rounded down to the nearest whole number) equal to the number of shares of Andeavor

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common stock subject to the Andeavor option immediately prior to the effective time multiplied by 1.87, which is referred to as the exchange ratio, at an exercise price per share (rounded up to the nearest whole cent) equal to the exercise price per Andeavor share of such Andeavor option divided by the exchange ratio. Following the effective time of the first merger, each such option will continue to be governed by the same terms and conditions as were applicable under such Andeavor option immediately prior to the effective time of the first merger.

Andeavor Restricted Stock Units

At the effective time of the first merger, each outstanding restricted stock unit award or phantom stock award in respect of Andeavor common stock with only time-based vesting requirements, except for awards held by non-employee directors of Andeavor, which is referred to as an Andeavor RSU, whether vested or unvested, will, automatically and without any action on the part of the holder thereof, cease to represent a restricted stock unit award or phantom stock award denominated in Andeavor common stock and be converted into a restricted stock unit award denominated in MPC common stock relating to the number of shares of MPC common stock (rounded down to the nearest whole number) equal to the number of shares of Andeavor common stock subject to such Andeavor RSU immediately prior to the effective time of the first merger multiplied by the exchange ratio. Following the effective time of the first merger, each such RSU will continue to be governed by the same terms and conditions as were applicable under such Andeavor RSU immediately prior to the effective time of the first merger.

Treatment of Andeavor Director Restricted Stock Units

At the effective time of the first merger, any vesting conditions applicable to each outstanding restricted stock unit award in respect of Andeavor common stock with only time-based vesting requirements that is held by a non-employee director of Andeavor, which is referred to as an Andeavor director RSU, will, automatically and without any required action on the part of the holder thereof, accelerate in full and be cancelled and will only entitle the holder of such Andeavor director RSU to receive (without interest), as soon as reasonably practicable following the effective time of the first merger (but in any event no later than 10 business days thereafter) an amount in cash equal to the number of shares of Andeavor common stock subject to such Andeavor director RSU multiplied by the cash consideration; provided, however, that to the extent that any such Andeavor director RSU constitutes nonqualified deferred compensation subject to Section 409A of the Internal Revenue Code, such cash payment will be paid in accordance with the applicable award’s terms and at the earliest time permitted under the terms of such award that will not result in the application of a tax or penalty under Section 409A of the Internal Revenue Code.

Treatment of Andeavor Performance Share Awards

At the effective time of the first merger, each outstanding performance share award with any performance-based vesting requirements, which is referred to as an Andeavor PSA, will, automatically and without any action on the part of the holder thereof, cease to represent a performance share award denominated in Andeavor common stock and be converted into a time-based restricted stock unit denominated in MPC common stock (rounded down to the nearest whole number) equal to the number of shares of Andeavor common stock that would have been issued under such Andeavor PSA assuming the greater of the achievement of target performance or the achievement of actual performance measured as of the effective time of the first merger, as reasonably determined in good faith by the compensation committee of the Andeavor board in accordance with the applicable award agreement and in consultation with the Chief Executive Officer of MPC, multiplied by the exchange ratio. Following the effective time of the first merger, each such RSU will continue to be governed by the same terms and conditions (including time-based vesting terms) as were applicable to such Andeavor PSA immediately prior to the effective time of the first merger.

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Treatment of Andeavor Market Stock Units

At the effective time of the first merger, each outstanding market stock unit in respect of Andeavor common stock, which is referred to as an Andeavor MSU, will, automatically and without any action on the part of the holder thereof, cease to represent a market stock unit award denominated in Andeavor common stock and be converted into a time-based restricted stock unit award denominated in MPC common stock (rounded down to the nearest whole number) equal to the greater of the target number of shares of Andeavor common stock subject to such Andeavor MSU or the number of shares of Andeavor common stock that would have been issued under such Andeavor MSU based on actual performance measured as of the effective time of the first merger, as reasonably determined in good faith by the compensation committee of the Andeavor board in accordance with the applicable award agreement and in consultation with the Chief Executive Officer of MPC, multiplied by the exchange ratio. Following the effective time of the first merger, each such RSU will continue to be governed by the same terms and conditions as were applicable to such Andeavor MSU immediately prior to the effective time of the first merger.

Treatment of Andeavor Restricted Shares

At the effective time of the first merger, each outstanding share of Andeavor common stock that is subject to vesting, repurchase, or other lapse of restrictions, which is referred to as an Andeavor restricted share, will, automatically and without any action on the part of the holder thereof, cease to represent an Andeavor restricted share and be converted into a number of restricted shares of MPC common stock (rounded down to the nearest whole number) equal to the number of Andeavor restricted shares held by the holder of such award, multiplied by the exchange ratio. Following the effective time of the first merger, each such restricted share will continue to be governed by the same terms and conditions (including vesting terms) as were applicable to such Andeavor restricted share immediately prior to the effective time of the first merger.

Other Company Awards

At the effective time of the first merger, each outstanding right of any kind, contingent or accrued, to acquire or receive shares of Andeavor common stock or benefits measured by the value of shares of Andeavor common stock, and each award of any kind consisting of shares of Andeavor common stock that may be held, awarded, outstanding, payable or reserved for issuance under the stock plans and any other Andeavor benefit plans other than Andeavor options, Andeavor RSUs, Andeavor director RSUs, Andeavor PSAs, Andeavor MSUs, and Andeavor restricted shares, which are referred to collectively as the Andeavor other awards, will, automatically and without any action on the part of the holder thereof, cease to represent an award denominated in Andeavor common stock and be converted into the right to acquire or receive benefits measured by the value of (as the case may be) the number of shares of MPC common stock (rounded down to the nearest whole number) equal to the product of the number of shares of Andeavor common stock subject to such Andeavor other award immediately prior to the effective time of the first merger multiplied by the exchange ratio. Following the effective time of the first merger, each such award will continue to be governed by the same terms and conditions as were applicable to such Andeavor other award immediately prior to the effective time of the first merger.

For more information regarding the treatment of Andeavor equity awards, see the section entitled “The Merger Agreement—Treatment of Andeavor Equity Awards in the Merger” beginning on page 154.

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Andeavor. The Andeavor board recommends that you vote “FOR” the approval of the Andeavor merger proposal, “FOR” the approval of the Andeavor compensation proposal and “FOR” the approval of the Andeavor adjournment proposal. For more information regarding how the Andeavor board recommends that you vote, see the section entitled “The Merger—Recommendation of the Andeavor Board and Reasons for the Merger” beginning on page 118.

Andeavor special meeting. The Andeavor board has fixed [                ], 2018 as the record date for the Andeavor special meeting. All holders of record of shares of Andeavor common stock as of the close of business on the record date are entitled to receive notice of, and to vote at, the Andeavor special meeting, provided that those shares remain outstanding on the date of the Andeavor special meeting. Physical attendance at the Andeavor special meeting is not required to vote. See the section entitled “Questions and Answers About the Merger and the Special Meetings—How can I vote my shares without attending the special meeting?” beginning on page 12 for instructions on how to vote your shares without attending the Andeavor special meeting.

MPC stockholders. If you are a stockholder of record of MPC common stock as of the close of business on the record date, and you vote via the Internet, by telephone or by signing, dating and returning your proxy card in the enclosed postage-paid envelope, you designate three of MPC’s officers as your proxies at the MPC special meeting, each with full power to act without the other and with full power of substitution. These three officers are Gary R. Heminger, Donald C. Templin and Timothy T. Griffith.

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Andeavor stockholders. If you are a stockholder of record of Andeavor common stock as of the close of business on the record date, and you vote via the Internet, by telephone or by signing, dating and returning your proxy card in the enclosed postage-paid envelope, you designate two of Andeavor’s officers as your proxies at the Andeavor special meeting, each with full power to act without the other and with full power of substitution. These two officers are Dathan C. Voelter and Elisa D. Watts.

Andeavor stockholders. Each Andeavor stockholder of record is entitled to one vote for each share of Andeavor common stock held of record by him or her as of the close of business on the record date.

Quorum for MPC special meeting. A quorum will exist at the MPC special meeting with respect to each matter to be considered at the MPC special meeting if the holders of a majority of shares of MPC common stock outstanding and entitled to vote as of the close of business on the record date are present in person or represented by proxy at the MPC special meeting. Shares of MPC common stock held in street name will be counted as present for the purpose of determining the existence of a quorum at the MPC special meeting so long as a stockholder has given the bank, broker or other nominee voting instructions on at least one of the proposals brought before the MPC special meeting. The proposals for consideration at the MPC special meeting are considered “non-routine” matters under NYSE Rule 452, and, therefore, no broker non-votes can occur at the meeting. A stockholder’s shares will not be counted as present for the purpose of determining the existence of a quorum if no instructions have been provided on how to vote on any such proposals.

Quorum for Andeavor special meeting. A quorum will exist at the Andeavor special meeting with respect to the matters to be considered at the Andeavor special meeting if the holders of a majority of shares of Andeavor common stock issued and outstanding and entitled to vote as of the close of business on the record date are present in person or represented by proxy at the Andeavor special meeting. Shares of Andeavor common stock held in street name will be counted as present for the purpose of determining the existence of a quorum at the Andeavor special meeting so long as a stockholder has given the broker or other nominee voting instructions on at least one of the proposals brought before the Andeavor special meeting. The proposals for consideration at the Andeavor special meeting are considered “non-routine” matters under NYSE Rule 452, and, therefore, no broker non-votes can occur at the meeting. A stockholder’s shares will not be counted as present for the purpose of determining the existence of a quorum if no instructions have been provided on how to vote on any such proposals.

Immediately following the completion of the first merger, the surviving corporation will merge with and into Merger Sub 2, which is referred to as the second merger. The first merger and the second merger are referred to together in this joint proxy statement/prospectus as the merger. Upon completion of the second merger, the separate corporate existence of Andeavor will cease as a result and Merger Sub 2 will continue as the surviving company and a wholly owned subsidiary of MPC, which is referred to as the surviving company.

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Andeavor stockholders become entitled to receive the per share merger consideration at the effective time of the first merger, on the terms and subject to the conditions set forth in the merger agreement.

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Failure to bring the appropriate documentation may delay your entry into or prevent you from attending the MPC special meeting. The doors to the meeting room will be closed promptly at the start of the MPC special meeting, and stockholders will not be permitted to enter after that time.

Andeavor. Shares of Andeavor common stock held directly in your name as the stockholder of record as of the close of business on [                ], 2018, the record date, may be voted in person at the Andeavor special meeting. If you choose to attend the Andeavor special meeting, you will need to bring valid, government-issued photo identification. If you are a beneficial owner of Andeavor common stock but not the stockholder of record of such shares of Andeavor common stock, you will also need proof of stock ownership to be admitted to the Andeavor special meeting. A recent brokerage statement or a letter from a bank or broker are examples of proof of ownership. Please note that if your shares are held in “street name” by a bank, broker or other nominee and you wish to vote at the Andeavor special meeting, you will not be permitted to vote in person unless you first obtain a legal proxy issued in your name from the record owner and present it to the inspector of election with your ballot at the Andeavor special meeting. To request a legal proxy,

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please contact your bank, broker or other nominee holder of record. It is suggested you do so in a timely manner to ensure receipt of your legal proxy prior to the Andeavor special meeting.

Please note that if your shares are held in the Andeavor 401(k) Plan, you may not vote in person at the Andeavor special meeting.

Failure to bring the appropriate documentation may delay your entry into or prevent you from attending the Andeavor special meeting. The doors to the meeting room will be closed promptly at the start of the Andeavor special meeting, and stockholders will not be permitted to enter after that time.

Andeavor. If you are a stockholder of record of Andeavor common stock as of the close of business on [            ], 2018, the record date, you can vote by proxy via the Internet, by telephone or by mail by following the instructions provided on the enclosed proxy card. Please note that if you are a beneficial owner, you may vote by submitting voting instructions to your bank, broker or other nominee, or otherwise by following instructions provided by your bank, broker or other nominee. Internet and telephone voting may be available to a beneficial owner. Please refer to the vote instruction form provided by your bank, broker or other nominee. If your shares are held in the Andeavor 401(k) Plan, you may not vote in person at the Andeavor special meeting. Participants in the Andeavor 401(k) Plan may instruct Fidelity Management Trust Company, as trustee for such plan, how to vote all shares of Andeavor common stock allocated to their accounts by following the instructions on the enclosed instruction card. If a participant in the Andeavor 401(k) Plan does not instruct Fidelity Management Trust Company how to vote, the shares of Andeavor common stock allocated to such participant’s accounts will not be voted.

Andeavor. If your shares of Andeavor common stock are registered directly in your name with Andeavor’s transfer agent, American Stock Transfer & Trust Company, you are considered the stockholder of record with respect to those shares, and access to proxy materials is being provided directly to you. If your shares are held by a bank, in a stock brokerage account or other nominee, then you are considered the beneficial owner of those shares, which are considered to be held in street name. Access to proxy materials is being provided to you by your bank, broker or other nominee who is considered the stockholder of record with respect to those shares. Shares of Andeavor common stock held in the Andeavor 401(k) Plan are considered held in street name.

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Direct holders (stockholders of record)

For shares of MPC and/or Andeavor common stock held directly, please complete, sign, date and return each proxy card (or cast your vote via the Internet or by telephone as provided on each proxy card) or otherwise follow the voting instructions provided in this joint proxy statement/prospectus in order to ensure that all of your shares of MPC and/or Andeavor common stock are voted.

Shares in “street name”

For shares of MPC and/or Andeavor common stock held in “street name” through a bank, broker or other nominee, you should follow the procedures provided by your bank, broker or other nominee to vote your shares.

Andeavor. If you sign, date and return your proxy and do not indicate how you want your shares of Andeavor common stock to be voted, then your shares of Andeavor common stock will be voted “FOR” the approval of the Andeavor merger proposal, “FOR” the approval of the Andeavor compensation proposal and “FOR” the approval of the Andeavor adjournment proposal.

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If you are a beneficial owner of MPC common stock as of the close of business on the record date, you must follow the instructions of your bank, broker or other nominee to revoke or change your voting instructions.

Andeavor. Yes. If you are a stockholder of record of Andeavor common stock as of the close of business on the record date, whether you vote via the Internet, by telephone or mail, you can change or revoke your proxy before it is voted at the Andeavor special meeting in one of the following ways:

If you are a beneficial owner of Andeavor common stock as of the close of business on the record date, you must follow the instructions of your bank, broker or other nominee to revoke or change your voting instructions.

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The full text of Section 262 of the DGCL is attached as Annex E to this joint proxy statement/prospectus. Andeavor stockholders are encouraged to read these provisions carefully and in their entirety. Moreover, due to the complexity of the procedures for exercising and perfecting the right to seek appraisal, Andeavor stockholders who are considering exercising and perfecting that right are encouraged to seek the advice of legal counsel. Failure to strictly comply with these provisions may result in a waiver of, or the inability to exercise, appraisal rights. For more information regarding appraisal rights, see the section entitled “Appraisal Rights of Andeavor Stockholders” beginning on page 220.

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Assuming the merger qualifies as a reorganization, a stockholder of Andeavor generally will not recognize any gain or loss upon receipt of MPC common stock in exchange for Andeavor common stock in the merger, will recognize gain (but not loss) in an amount not to exceed any cash received as part of the cash consideration (other than cash received in lieu of a fractional share) and will recognize gain or loss with respect to any cash received in lieu of a fractional share of MPC common stock. The U.S. federal income tax consequences of the merger are discussed in more detail in the section entitled “Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 186. The discussion of the material U.S. federal income tax consequences contained in this joint proxy statement/prospectus is intended to provide only a general discussion and is not a complete analysis or description of all potential U.S. federal income tax consequences of the merger that may vary with, or are dependent on, individual circumstances. In addition, it does not address the effects of any foreign, state or local tax laws.

TAX MATTERS ARE COMPLICATED AND THE TAX CONSEQUENCES OF THE MERGER WILL DEPEND ON THE FACTS OF YOUR OWN SITUATION. YOU SHOULD CONSULT YOUR OWN TAX ADVISOR AS TO THE SPECIFIC TAX CONSEQUENCES OF THE MERGER TO YOU IN YOUR PARTICULAR CIRCUMSTANCES.

Andeavor. Andeavor has retained Innisfree to assist in the solicitation process. Andeavor will pay Innisfree a fee of approximately $25,000, as well as reasonable and documented out-of-pocket expenses. Andeavor also has agreed to indemnify Innisfree against various liabilities and expenses that relate to or arise out of its solicitation of proxies (subject to certain exceptions).

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After receiving the proper documentation from you, following the effective time, the exchange agent will deliver to you the cash consideration or stock consideration (plus, in the case of stock consideration, any cash in lieu of fractional shares and any applicable dividends on MPC common stock with a record date after the merger is completed) to which you are entitled. More information on the documentation you are required to deliver to the exchange agent can be found in the section entitled “The Merger Agreement—Election and Exchange Procedures” beginning on page 156.

For the past three years, MPC has paid a quarterly dividend on the MPC common stock as described in greater detail in the section entitled “Comparative Per Share Market Price and Dividend Information—MPC

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Market Price and Dividend Information” beginning on page 44. MPC last declared a dividend on April 25, 2018, in an amount of $0.46 per MPC share, which was paid on June 11, 2018 to MPC stockholders of record as of the close of business on May 16, 2018. Any future MPC dividends will remain subject to approval by the MPC board.

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This registration statement on Form S-4, of which this joint proxy statement/prospectus forms a part, and the documents to which Andeavor and MPC refer you in this registration statement, of which this joint proxy statement/prospectus forms a part, as well as oral statements made or to be made by Andeavor and MPC, include certain “forward-looking statements” within the meaning of, and subject to the safe harbor created by, Section 27A of the Securities Act of 1933 and Section 21E of the Exchange Act, which are referred to as the safe harbor provisions. Words such as “anticipate,” “assume,” “believe,” “build,” “continue,” “create,” “design,” “estimate,” “expect,” “focus,” “forecast,” “future,” “goal,” “guidance,” “imply,” “intend,” “look,” “objective,” “opportunity,” “outlook,” “plan,” “position,” “potential,” “predict,” “project,” “prospective,” “pursue,” “seek,” “strategy,” “target,” “work,” “could,” “may,” “should,” “would,” “will” or the negative of such terms or other variations thereof and words and terms of similar substance used in connection with any discussion of future plans, actions, or events identify forward-looking statements with respect to the businesses, strategies and plans of Andeavor and MPC, their expectations relating to the merger and their future financial condition and performance. MPC and Andeavor caution investors that any forward-looking statements are subject to risks and uncertainties that may cause actual results and future trends to differ materially from those matters expressed in or implied by such forward-looking statements. Investors are cautioned not to place undue reliance on forward-looking statements. Among the risks and uncertainties that could cause actual results to differ from those described in forward-looking statements are the following:

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Such factors are difficult to predict and in many cases may be beyond the control of MPC and Andeavor. MPC’s and Andeavor’s forward-looking statements are based on assumptions that MPC and Andeavor, respectively, believe to be reasonable but that may not prove to be accurate. Consequently, all of the forward-looking statements MPC and Andeavor make in this document are qualified by the information contained or incorporated by reference herein, including the information contained under this heading and the information detailed in MPC’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017 and MPC’s Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2018, and in Andeavor’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017 and Andeavor’s Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2018. See the section entitled “Where You Can Find More Information” beginning on page 234.

MPC and Andeavor undertake no obligation to publicly release the result of any revisions to any such forward-looking statements that may be made to reflect events or circumstances that occur, or which they become aware of, except as required by applicable law or regulation. Readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof.

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RISK FACTORS

In addition to the other information contained in or incorporated by reference herein, including the matters addressed in the section entitled “Cautionary Statement Regarding Forward-Looking Statements” beginning on page 47, Andeavor stockholders should carefully consider the following risks before deciding how to vote with respect to the proposals to be considered and voted on at the Andeavor special meeting, and MPC stockholders should carefully consider the following risks before deciding how to vote with respect to the proposals to be considered and voted on at the MPC special meeting. Andeavor and MPC stockholders should also consider the other information in this joint proxy statement/prospectus and the other documents incorporated by reference herein, particularly the risk factors contained in MPC’s and Andeavor’s Annual Reports on Form 10-K and Quarterly Reports on Form 10-Q. See the section entitled “Where You Can Find More Information” beginning on page 234.

Risks Relating to the Merger

Because the market price of shares of MPC common stock may fluctuate, Andeavor stockholders cannot be certain of the precise value of any stock consideration they may receive in the merger.

At the time the merger is completed, each issued and outstanding share of Andeavor common stock (other than excluded shares as defined in the section entitled “The Merger—Consideration to Andeavor Stockholders” beginning on page 78) will be converted into the right to receive either the cash consideration of $152.27, if the Andeavor stockholder makes a cash election, or the stock consideration of 1.87 shares of MPC common stock, if the Andeavor stockholder makes or is deemed to have made a stock election. Both the cash election and the stock election are subject to the allocation and proration procedures set forth in the merger agreement. The exchange ratio for the stock consideration is fixed, and there will be no adjustment to the stock consideration for changes in the market price of shares of MPC common stock or Andeavor common stock prior to the completion of the merger. If the merger is completed, there will be a time lapse between each of the date of this joint proxy statement/prospectus, the dates on which Andeavor stockholders vote to approve the Andeavor merger proposal at the Andeavor special meeting and MPC stockholders vote to approve the MPC issuance proposal at the MPC special meeting, and the date on which Andeavor stockholders entitled to receive the stock consideration actually receive such stock consideration. The market value of shares of MPC common stock may fluctuate during and after these periods as a result of a variety of factors (many of which are outside of MPC’s or Andeavor’s control), including general market and economic conditions, changes in MPC’s businesses, operations and prospects and regulatory considerations. Such factors are difficult to predict and in many cases may be beyond the control of MPC and Andeavor. Consequently, at the time Andeavor stockholders must decide whether to adopt the merger agreement, and make their elections to receive the cash consideration or stock consideration, they will not know the actual market value of any stock consideration they will receive when the merger is completed. The actual value of any stock consideration received by Andeavor stockholders at the completion of the merger will depend on the market value of the shares of MPC common stock at that time. This market value may differ, possibly materially, from the market value of shares of MPC common stock at the time the merger agreement was entered into or at any other time. Andeavor stockholders should obtain current stock quotations for shares of MPC common stock before voting their shares of Andeavor common stock. For additional information about the Andeavor per share merger consideration, see the section entitled “The Merger Agreement—Merger Consideration” beginning on page 153.

The value of the cash consideration and the stock consideration may differ considerably.

Since the cash consideration is a fixed amount of $152.27 and the market value of the stock consideration will continuously change with the market price for MPC common stock, it is possible that, at the time of the MPC special meeting, the election deadline, the effective time of the first merger and/or any other time, the cash consideration could be worth more, less or the same amount as the stock consideration. Further, because you will not be able to change your election after the election deadline (and because of the allocation and proration

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procedures discussed below), you may receive per share merger consideration that is worth less than the other per share merger consideration you could have elected, even if the per share merger consideration you elected to receive is worth more at the election deadline than the per share merger consideration you actually receive. Additionally, since cash elections are subject to proration, in the event the cash consideration is worth more than the stock consideration, Andeavor stockholders may not be able to realize the excess of such difference even if they make a cash election with respect to all of their shares of Andeavor common stock. Similarly, since stock elections are subject to proration, in the event the stock consideration is worth more than the cash consideration, Andeavor stockholders may not be able to realize the excess of such difference even if they make a stock election with respect to all of their shares of Andeavor common stock.

The market price of shares of MPC common stock will continue to fluctuate after the merger.

Upon completion of the merger, holders of Andeavor common stock who receive stock consideration will become holders of shares of MPC common stock. The market price of shares of MPC common stock may fluctuate significantly following completion of the merger and holders of Andeavor common stock could lose some or all of the value of their investment in MPC common stock. In addition, the stock market has experienced significant price and volume fluctuations in recent times which, if they continue to occur, could have a material adverse effect on the market for, or liquidity of, the MPC common stock, regardless of MPC’s actual operating performance.

Andeavor stockholders may receive a form of consideration different from what they elect.

Although each Andeavor stockholder may elect, for each share of Andeavor common stock he or she owns that is issued and outstanding as of immediately prior to the effective time of the first merger (other than excluded shares as defined in the section entitled “The Merger—Consideration to Andeavor Stockholders” beginning on page 78), to receive the cash consideration or the stock consideration in the first merger, the aggregate amounts of cash consideration and stock consideration to be paid in the first merger are subject to the allocation and proration procedures set forth in the merger agreement to ensure that the total number of shares of Andeavor stock converted into the right to receive the cash consideration in the first merger will be fixed at 22,885,359 shares of Andeavor stock issued and outstanding immediately prior to the closing of the first merger. As a result, if Andeavor stockholders make a cash election in respect of more than the cash election number of shares of Andeavor common stock, which is referred to as an oversubscription of the cash election, Andeavor stockholders who have elected cash consideration will receive stock consideration in exchange for some or all of the shares of Andeavor common stock in respect of which they have made cash elections. Similarly, if Andeavor stockholders make a stock election in respect of more than the total number of shares of Andeavor common stock to be converted in connection with the merger less the cash election number, which is referred to as an oversubscription of the stock election, Andeavor stockholders who have elected stock consideration will receive cash consideration in exchange for some or all of the shares of Andeavor common stock in respect of which they have made stock elections. In some cases, due to rounding, the pro rata portion held by a particular holder may be zero, such that none of such shares of Andeavor common stock held by such holder will be converted into the right to receive either the cash or stock consideration, as applicable. The receipt of a form of consideration other than that elected by an Andeavor stockholder could result in, among other things, tax consequences that differ from those that would have resulted if such stockholders had received the form of consideration that they had elected. For a more detailed description of how the allocation and proration procedures would work in the event that there is an oversubscription of either the cash election or the stock election, see the section entitled “The Merger Agreement—Merger Consideration” beginning on page 153.

After an Andeavor stockholder has made an election in respect of his or her shares of Andeavor common stock, he or she will not be able to sell those shares unless he or she revokes his or her election prior to the election deadline or the merger agreement is terminated.

To be effective, a form of election must be properly completed, signed and submitted to the exchange agent by 5:00 p.m. Eastern Time on the business day that is two trading days prior to the closing date for the first

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merger, or such other date and time as MPC may publicly announce with the consent of Andeavor. The closing date of the first merger will be publicly announced by MPC at least four business days prior to the anticipated closing date of the first merger. After an Andeavor stockholder has submitted a form of election, under the terms of the election, he or she will not be able to sell any Andeavor shares covered by his or her form of election, regardless of whether those Andeavor shares are held in certificated or book-entry form, unless he or she revokes his or her election before the deadline by written notice received by the exchange agent prior to the election deadline. While the parties have agreed to establish an election deadline that is a relatively short time before the anticipated completion date of the first merger, there can be no assurance that unforeseen circumstances will not cause the completion of the first merger to be delayed after the deadline has been established.

Andeavor stockholders will have a reduced ownership and voting interest in the combined company after the merger and will exercise less influence over management.

Currently, Andeavor stockholders have the right to vote in the election of the Andeavor board and the power to approve or reject any matters requiring stockholder approval under Delaware law and Andeavor’s certificate of incorporation and bylaws. Upon completion of the merger, each Andeavor stockholder who receives shares of MPC common stock in the merger will become a stockholder of MPC with a percentage ownership of MPC that is smaller than the Andeavor stockholder’s current percentage ownership of Andeavor. Based on the number of issued and outstanding shares of MPC common stock and shares of Andeavor common stock as of April 26, 2018 and on the exchange ratio of 1.87, with 22,885,359 shares of Andeavor common stock in the aggregate converted into the right to receive cash consideration, after the merger, Andeavor stockholders are expected to become owners of approximately 34% of the outstanding shares of MPC common stock, without giving effect to any shares of MPC common stock held by Andeavor stockholders prior to the completion of the merger. Even if all former Andeavor stockholders voted together on all matters presented to MPC stockholders from time to time, the former Andeavor stockholders would exercise significantly less influence over MPC after the completion of the merger relative to their influence over Andeavor prior to the completion of the merger, and thus would have a less significant impact on the election of the MPC board and on the approval or rejection of future MPC proposals submitted to a stockholder vote.

Shares of MPC common stock received by Andeavor stockholders as a result of the merger will have different rights from shares of Andeavor common stock.

Upon completion of the merger, Andeavor stockholders will no longer be stockholders of Andeavor, and Andeavor stockholders who receive stock consideration will become stockholders of MPC. There will be important differences between the current rights of Andeavor stockholders and the rights to which such stockholders will be entitled as stockholders of MPC. See the section entitled “Comparison of Stockholders’ Rights” beginning on page 207 for a discussion of the different rights associated with the shares of MPC common stock.

The market price of shares of MPC common stock may be affected by factors different from those that historically have affected shares of Andeavor common stock.

Upon completion of the merger, holders of Andeavor common stock who receive stock consideration will become holders of MPC common stock. The businesses of MPC differ from those of Andeavor in certain respects, and, accordingly, the financial position or results of operations and/or cash flows of MPC after the merger, as well as the market price of shares of MPC common stock, may be affected by factors different from those currently affecting the financial position or results of operations and/or cash flows of Andeavor. Following the completion of the merger, Andeavor will be part of a larger company with other lines of business and a broader geographic footprint, so decisions affecting Andeavor may be made in respect of the larger combined business as a whole rather than the Andeavor businesses individually. For a discussion of the businesses of MPC and Andeavor and of some important factors to consider in connection with those businesses, see the section entitled “Information About the Companies” beginning on page 61, and the documents incorporated by reference

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in the section entitled “Where You Can Find More Information” beginning on page 234, including, in particular, in the sections entitled “Risk Factors” in each of MPC’s Annual Report on Form 10-K for the year ended December 31, 2017, Andeavor’s Annual Report on Form 10-K for the year ended December 31, 2017 and Andeavor’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2018.

The merger agreement limits MPC’s ability and Andeavor’s ability to pursue alternatives to the merger.

The merger agreement contains provisions that may discourage a third party from submitting an acquisition proposal to MPC or Andeavor that might result in greater value to MPC’s or Andeavor’s respective stockholders than the merger, or may result in a potential acquirer of MPC, or a potential competing acquirer of Andeavor, proposing to pay a lower per share price to acquire MPC or Andeavor, respectively, than it might otherwise have proposed to pay. These provisions include a general prohibition on MPC and Andeavor from soliciting or, subject to certain exceptions relating to the exercise of fiduciary duties by the MPC board or the Andeavor board, entering into discussions with any third party regarding any acquisition proposal or offer for a competing transaction. Andeavor also has an unqualified obligation to submit the Andeavor merger proposal to a vote by its stockholders, even if Andeavor receives an alternative acquisition proposal that the Andeavor board believes is superior to the merger, and MPC has an unqualified obligation to submit the MPC issuance proposal to a vote by its stockholders, even if MPC receives an alternative acquisition proposal that the MPC board believes is superior to the merger, in each case unless Andeavor or MPC, as applicable, terminates the merger agreement in accordance with its terms prior to such time. See the section entitled “The Merger Agreement—Termination” beginning on page 179.

The merger agreement may be terminated in accordance with its terms and the merger may not be completed.

The merger agreement is subject to a number of conditions that must be fulfilled in order to complete the merger. Those conditions include, among others: the adoption of the merger agreement by Andeavor stockholders, the approval by MPC stockholders of the issuance of shares of MPC common stock in connection with the merger, the approval to list MPC common stock issuable in connection with the merger on the NYSE, the expiration or termination of the waiting period applicable to the merger under the HSR Act, as well as the satisfaction of all approvals, notices or other requirements under other antitrust laws, without the imposition of a burdensome condition (as defined in the section entitled “The Merger Agreement—Reasonable Best Efforts; Regulatory Filings and Other Actions—Burdensome Condition” beginning on page 173 and in the merger agreement), the absence of any governmental order or law prohibiting the consummation of the merger, effectiveness of the registration statement of which this joint proxy statement/prospectus forms a part, the accuracy of representations and warranties under the merger agreement (subject to the materiality standards set forth in the merger agreement), MPC’s and Andeavor’s performance of their respective obligations under the merger agreement in all material respects, the absence of a material adverse effect for MPC (as described in the merger agreement), the absence of a material adverse effect for Andeavor (as described in the merger agreement) and Andeavor’s receipt of a written opinion of Sullivan & Cromwell LLP (or another nationally recognized law firm selected by Andeavor) regarding the U.S. federal income tax treatment of the transaction. These conditions to the closing of the merger may not be fulfilled in a timely manner or at all, and, accordingly, the merger may be delayed or may not be completed.

In addition, if the merger is not completed by April 29, 2019, either MPC or Andeavor may choose not to proceed with the merger, and the parties can mutually decide to terminate the merger agreement at any time, before or after stockholder approval. In addition, MPC and Andeavor may elect to terminate the merger agreement in certain other circumstances. See the section entitled “The Merger Agreement—Termination” beginning on page 179.

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Failure to complete the merger could negatively impact the price of shares of MPC common stock and the price of shares of Andeavor common stock, as well as MPC’s and Andeavor’s respective future businesses and financial results.

The merger agreement contains a number of conditions that must be satisfied or waived prior to the completion of the merger. There can be no assurance that all of the conditions to the merger will be so satisfied or waived. If the conditions to the merger are not satisfied or waived, MPC and Andeavor will be unable to complete the merger and the merger agreement may be terminated.

If the merger is not completed for any reason, including the failure to receive the required approvals of MPC’s and Andeavor’s respective stockholders, MPC’s and Andeavor’s respective businesses and financial results may be adversely affected as follows:

In addition to the above risks, if the merger agreement is terminated and either party’s board seeks an alternative transaction, such party’s stockholders cannot be certain that such party will be able to find a party willing to engage in a transaction on more attractive terms than the merger. If the merger agreement is terminated under specified circumstances, either MPC or Andeavor may be required to pay the other party a termination fee, reverse termination fee or other termination-related payment. See the section entitled “The Merger Agreement—Termination” beginning on page 179 for a description of these circumstances.

Required regulatory approvals may impose conditions that are not presently anticipated or cannot be met. In addition, an adverse outcome of any antitrust or similar review undertaken by a governmental authority could prevent the merger from being completed or have an adverse effect on MPC following the merger.

Completion of the merger is conditioned upon the approval by the NYSE of the listing of the shares of MPC

common stock to be issued in the merger upon official notice of issuance and the expiration or termination of the

waiting period applicable to the merger under the HSR Act.

The waiting period applicable to the merger under the HSR Act expired on July 2, 2018.

Even though the waiting period expired under the HSR Act, the FTC or the Antitrust Division of the DOJ could take action under antitrust laws to prevent or rescind the merger, require the divestiture of assets, impose conditions on the completion of the merger or require changes to the terms of the merger or merger agreement. Such conditions or changes and the process of obtaining regulatory approvals could have the effect of delaying or impeding completion of the merger or of imposing additional costs or limitations on MPC following completion of the merger, any of which might have an adverse effect on MPC following completion of the merger. Additionally, state attorneys general could seek to block or challenge the merger as they deem necessary or desirable in the public interest at any time, including after completion of the merger. In addition, in some circumstances, a third party could initiate a private action under antitrust laws challenging or seeking to enjoin the merger, before or after it is completed.

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The obligation of each of MPC and Andeavor to effect the merger is also subject to obtaining regulatory approval in Canada. On June 1, 2018, MPC and Andeavor submitted notifications and an application for Competition Bureau of Canada clearance of the merger and the parties received the necessary regulatory clearance in Canada on June 16, 2018.

MPC and Andeavor will be subject to business uncertainties while the merger is pending, which could adversely affect their respective businesses.

Uncertainty about the effect of the merger on employees and customers may have an adverse effect on MPC and Andeavor. These uncertainties may impair MPC’s and Andeavor’s ability to attract, retain and motivate key personnel until the merger is completed and for a period of time thereafter, and could cause customers and others that deal with MPC and Andeavor to seek to change their existing business relationships with MPC and Andeavor, respectively. Employee retention at Andeavor may be particularly challenging during the pendency of the merger, as employees may experience uncertainty about their roles with MPC following the merger. In addition, the merger agreement restricts MPC and Andeavor from entering into certain corporate transactions and taking other specified actions without the consent of the other party, and generally requires Andeavor to continue its operations in the ordinary course, until completion of the merger. These restrictions may prevent MPC and Andeavor from pursuing attractive business opportunities that may arise prior to the completion of the merger. Please see the section entitled “The Merger Agreement—Interim Operations of Andeavor and MPC Pending the Merger,” beginning on page 163, for a description of the restrictive covenants to which MPC and Andeavor are subject.

Directors and executive officers of Andeavor may have interests in the merger that are different from, or in addition to, the interests of Andeavor stockholders.

Directors and executive officers of Andeavor may have interests in the merger that are different from, or in addition to, the interests of Andeavor stockholders generally. These interests include, among others, the treatment of outstanding equity and equity-based awards pursuant to the merger agreement; potential severance and other benefits upon a qualifying termination in connection with the merger; MPC’s agreement to nominate four current members of the Andeavor board for election as directors of MPC, with terms commencing upon the completion of the merger; and rights to ongoing indemnification and insurance coverage. These interests are described in more detail in the section entitled “The Merger—Interests of Andeavor Directors and Executive Officers in the Merger” beginning on page 144.

The merger may not be accretive, and may be dilutive, to MPC’s earnings per share and cash flow from operations per share, which may negatively affect the market price of shares of MPC common stock.

The merger may not be accretive, and may be dilutive, to MPC’s earnings per share and cash flow from operations per share. Earnings per share and cash flow from operations per share in the future are based on preliminary estimates that may materially change. In addition, future events and conditions could decrease or delay any accretion, result in dilution or cause greater dilution than is currently expected, including:

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Any dilution of, or decrease or delay of any accretion to, MPC’s earnings per share or cash flow from operations per share could cause the price of MPC’s common stock to decline.

MPC and Andeavor will incur significant transaction and merger-related costs in connection with the merger, which may be in excess of those anticipated by MPC or Andeavor.

Each of MPC and Andeavor has incurred and will incur substantial expenses in connection with the negotiation and completion of the transactions contemplated by the merger agreement, including the costs and expenses of filing, printing and mailing this joint proxy statement/prospectus and all filing and other fees paid to the SEC in connection with the merger.

MPC and Andeavor expect to continue to incur a number of non-recurring costs associated with completing the merger, combining the operations of the two companies and achieving desired synergies. These fees and costs have been, and will continue to be, substantial. The substantial majority of non-recurring expenses will consist of transaction costs related to the merger and include, among others, employee retention costs, fees paid to financial, legal and accounting advisors, severance and benefit costs and filing fees.

MPC and Andeavor will also incur transaction fees and costs related to formulating and implementing integration plans, including facilities and systems consolidation costs and employment-related costs. MPC and Andeavor will continue to assess the magnitude of these costs, and additional unanticipated costs may be incurred in the merger and the integration of the two companies’ businesses. Although MPC and Andeavor each expects that the elimination of duplicative costs, as well as the realization of other efficiencies related to the integration of the businesses, should allow MPC and Andeavor to offset integration-related costs over time, this net benefit may not be achieved in the near term, or at all. See the risk factor entitled “The integration of Andeavor into MPC may not be as successful as anticipated” below.

The costs described above, as well as other unanticipated costs and expenses, could have a material adverse effect on the financial condition and operating results of MPC following the completion of the merger.

Many of these costs will be borne by MPC and/or Andeavor even if the merger is not completed.

Lawsuits have been filed against Andeavor and the members of the Andeavor Board challenging the adequacy of the disclosures made in the initial version of the joint proxy statement/prospectus filed on May 29, 2018, and an adverse ruling in one or more of these lawsuits may prevent the merger from being completed.

As of June 29, 2018, Andeavor and the members of the Andeavor board have been named as defendants in five purported stockholder class actions challenging the adequacy of the disclosures to Andeavor stockholders made in the initial version of the joint proxy statement/prospectus filed on May 29, 2018. Two complaints were filed in the U.S. District Court for the Western District of Texas and the other three complaints were filed in the U.S. District Court for the District of Delaware.

Additional lawsuits arising out of the merger may be filed in the future. There can be no assurance that any of the defendants will be successful in the outcome of the pending or any potential future lawsuits. A preliminary injunction could delay or jeopardize the completion of the merger, and an adverse judgment granting permanent injunctive relief could indefinitely enjoin the completion of the merger.

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The opinions of MPC’s and Andeavor’s respective financial advisors will not reflect changes in circumstances between the signing of the merger agreement and the completion of the merger.

MPC and Andeavor have received opinions from their respective financial advisors in connection with the signing of the merger agreement, but have not requested or obtained, and do not intend to request, updated opinions from their respective financial advisors as of the date of this joint proxy statement/prospectus. Changes in the operations and prospects of MPC or Andeavor, general market and economic conditions and other factors that may be beyond the control of MPC or Andeavor, and on which MPC’s and Andeavor’s financial advisors’ opinions were based, may significantly alter the value of MPC or Andeavor or the prices of the shares of MPC common stock or of the shares of Andeavor common stock by the time the merger is completed. The opinions do not speak as of the time the merger will be completed or as of any date other than the dates referenced in such opinions. Because MPC and Andeavor do not currently anticipate asking their respective financial advisors to update their opinions, the opinions will not address the fairness of the per share merger consideration or aggregate merger consideration, as applicable, from a financial point of view at the time the merger is completed. The MPC board’s recommendation that MPC stockholders vote “FOR” approval of the MPC issuance proposal and the other merger-related matters and the Andeavor board’s recommendation that Andeavor stockholders vote “FOR” adoption of the merger agreement and the other merger-related matters, however, is made as of the date of this joint proxy statement/prospectus. For a description of the opinions that MPC and Andeavor received from their respective financial advisors, please see the sections entitled “The Merger—Opinion of Barclays, MPC’s Financial Advisor” and “The Merger—Opinion of Goldman Sachs, Andeavor’s Financial Advisor” beginning on pages 92 and 123, respectively. A copy of the opinion of Barclays, MPC’s financial advisor, is attached as Annex C to this joint proxy statement/prospectus, and a copy of the opinion of Goldman Sachs, Andeavor’s financial advisor, is attached as Annex D to this joint proxy statement/prospectus, and each is incorporated by reference herein in its entirety.

Completion of the merger may trigger change in control or other provisions in certain agreements to which Andeavor is a party.

The completion of the merger may trigger change in control or other provisions in certain agreements to which Andeavor is a party. If MPC and Andeavor are unable to negotiate waivers of those provisions, the counterparties may exercise their rights and remedies under the agreements, potentially terminating the agreements or seeking monetary damages. Even if MPC and Andeavor are able to negotiate waivers, the counterparties may require a fee for such waivers or seek to renegotiate the agreements on terms less favorable to Andeavor.

The combined company’s debt may limit its financial flexibility.

As of March 31, 2018, MPC had approximately $17.8 billion of outstanding indebtedness, including approximately $12.4 billion of obligations of MPLX. As of March 31, 2018, Andeavor had approximately $8.8 billion of outstanding indebtedness, including approximately $4.2 billion of obligations of Andeavor Logistics. MPC continues to review the treatment of its and Andeavor’s existing indebtedness and MPC may seek to repay, refinance, repurchase, redeem, exchange or otherwise terminate its or Andeavor’s existing indebtedness prior to, in connection with or following the completion of the merger. If MPC does seek to refinance its or Andeavor’s existing indebtedness, there can be no guarantee that MPC would be able to execute the refinancing on favorable terms or at all. Assuming MPC does not repay, repurchase, redeem, exchange or otherwise terminate any of its or Andeavor’s existing indebtedness, immediately following the completion of the merger, MPC is expected to have outstanding indebtedness of approximately $27.7 billion, based on MPC’s and Andeavor’s outstanding indebtedness as of March 31, 2018.

Any increase in MPC’s indebtedness could have adverse effects on its financial condition and results of operations, including:

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In addition, in connection with executing MPC’s business strategies following the merger, MPC expects to continue to evaluate the possibility of acquiring additional assets and making further strategic investments, and MPC may elect to finance these endeavors by incurring additional indebtedness.

MPC’s ability to arrange any additional financing for the purposes described above or otherwise will depend on, among other factors, the company’s financial position and performance, as well as prevailing market conditions and other factors beyond MPC’s control. MPC cannot assure you that it will be able to obtain such financing on terms acceptable to MPC or at all.

The unaudited pro forma condensed consolidated combined financial information and unaudited forecasted financial information included in this joint proxy statement/prospectus is presented for illustrative purposes only and does not represent the actual financial position or results of operations of the combined company following the completion of the merger. Future results of MPC or Andeavor may differ, possibly materially, from the unaudited pro forma condensed consolidated combined financial information and unaudited forecasted financial information presented in this joint proxy statement/prospectus.

The unaudited pro forma condensed consolidated combined financial statements and unaudited forecasted financial information contained in this joint proxy statement/prospectus is presented for illustrative purposes only, contains a variety of adjustments, assumptions and preliminary estimates and does not represent the actual financial position or results of operations of MPC and Andeavor prior to the merger or that of the combined company following the merger for several reasons. Specifically, we have not completed the detailed valuation analyses to arrive at the final estimates of the fair values of the assets to be acquired and liabilities to be assumed and the related allocation of purchase price and the unaudited pro forma condensed consolidated combined financial statements do not reflect the effects of transaction-related costs and integration costs. See the sections entitled “Unaudited Pro Forma Condensed Consolidated Combined Financial Statements”, and “Notes to Unaudited Pro Forma Condensed Consolidated Combined Financial Statements” beginning on pages 190 and 195, respectively. In addition, the merger and post-merger integration process may give rise to unexpected liabilities and costs, including costs associated with the defense and resolution of transaction-related litigation or other claims. Unexpected delays in completing the merger or in connection with the post-merger integration process may significantly increase the related costs and expenses incurred by MPC. The actual financial positions and results of operations of MPC and Andeavor prior to the merger and that of the combined company following the merger may be different, possibly materially, from the unaudited pro forma condensed consolidated combined financial statements or forecasted financial information included in this joint proxy statement/prospectus. In addition, the assumptions used in preparing the unaudited pro forma condensed consolidated combined financial statements and forecasted financial information included in this joint proxy statement/prospectus may not prove to be accurate and may be affected by other factors. Any significant changes in the market price of MPC common stock may cause a significant change in the purchase price used for MPC’s accounting purposes and the unaudited pro forma financial statements contained in this joint proxy statement/prospectus.

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The impact of the recent significant federal tax reform on the combined company is uncertain and may significantly affect the operations of the combined company after the merger.

On December 22, 2017, the President signed the budget reconciliation act commonly referred to as the Tax Cuts and Jobs Act, which is referred to as the TCJA, into law. The TCJA makes broad and complex changes to the U.S. tax code. The TCJA will change how the combined company’s earnings are taxed, including, among other items, (1) reducing the U.S. federal corporate tax rate from 35 percent to 21 percent; (2) repealing the corporate alternative minimum tax and changing how existing credits can be utilized; (3) temporarily providing for elective immediate expensing for certain depreciable property; (4) creating a new limitation on the deductibility of interest expense; and (5) changing rules related to uses and limitations of net operating losses created in tax years beginning after December 31, 2017. MPC and Andeavor continue to evaluate the TCJA and its impact on the combined company’s businesses. It is possible that the TCJA will be subject to further changes either in a technical corrections bill or entirely new legislation. The overall impact of the TCJA also depends on the future interpretations and regulations that may be issued by U.S. tax authorities. We expect there will be further guidance provided by these authorities potentially having a material adverse effect on our combined financial condition or results of operations. The impact of broad proposals or of regulatory issuances on our business can vary substantially depending upon the specific changes or further guidance made and how the changes or guidance are implemented by the authorities.

The integration of Andeavor into MPC may not be as successful as anticipated.

The merger involves numerous operational, strategic, financial, accounting, legal, tax and other risks; potential liabilities associated with the acquired businesses; and uncertainties related to design, operation and integration of Andeavor’s internal control over financial reporting. Difficulties in integrating Andeavor into MPC may result in Andeavor performing differently than expected, in operational challenges or in the failure to realize anticipated expense-related efficiencies. MPC’s and Andeavor’s existing businesses could also be negatively impacted by the merger. Potential difficulties that may be encountered in the integration process include, among other factors:

MPC’s results may suffer if it does not effectively manage its expanded operations following the merger.

Following completion of the merger, MPC’s success will depend, in part, on its ability to manage its expansion, which poses numerous risks and uncertainties, including the need to integrate the operations and business of Andeavor into its existing business in an efficient and timely manner, to combine systems and management controls and to integrate relationships with customers, vendors and business partners.

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Even if MPC and Andeavor complete the merger, MPC may fail to realize all of the anticipated benefits of the proposed merger.

The success of the proposed merger will depend, in part, on MPC’s ability to realize the anticipated benefits and cost savings from combining MPC’s and Andeavor’s businesses, including the approximately $1 billion in annual gross, run-rate, commercial and corporate synergies that MPC expects the combined company to realize within the first three years after the combination. The anticipated benefits and cost savings of the proposed merger may not be realized fully or at all, may take longer to realize than expected, may require more non-recurring costs and expenditures to realize than expected or could have other adverse effects that MPC does not currently foresee. Some of the assumptions that MPC has made, such as with respect to anticipated: operating synergies or the costs associated with realizing such synergies; significant long-term cash flow generation; the benefit from a substantial increase in scale and geographic diversity; complementary growth platforms for both midstream and retail businesses; positioning for potentially significant benefits from the International Maritime Organization change in specifications for marine bunker fuel; the expansion in opportunities for logistics growth in crude oil production basins and regions; further optimization of crude supply; and the continuation of MPC’s investment grade credit profile, may not be realized. The integration process may, for each of MPC and Andeavor, result in the loss of key employees, the disruption of ongoing businesses or inconsistencies in standards, controls, procedures and policies. There could be potential unknown liabilities and unforeseen expenses associated with the merger that were not discovered in the course of performing due diligence.

Uncertainties associated with the merger may cause a loss of management personnel and other employees, which could adversely affect the future business and operations of the combined company.

MPC and Andeavor are dependent on the experience and industry knowledge of their officers and other employees to execute their business plans. Each company’s success until the merger and the combined company’s success after the merger will depend in part upon the ability of MPC and Andeavor to retain management personnel and other employees. Current and prospective employees of MPC and Andeavor may experience uncertainty about their roles within the combined company following the merger, which may have an adverse effect on the ability of each of MPC and Andeavor to attract or retain management and other personnel. Accordingly, no assurance can be given that the combined company will be able to attract or retain management, personnel and other employees of MPC and Andeavor to the same extent that MPC and Andeavor have previously been able to attract or retain their own employees.

The market price of shares of MPC common stock may decline in the future as a result of the sale of shares of MPC common stock held by former Andeavor stockholders or current MPC stockholders.

Based on the number of shares of Andeavor common stock outstanding as of April 26, 2018 (other than excluded shares), MPC expects to issue up to approximately 240 million shares of MPC common stock to Andeavor stockholders in the merger. Following their receipt of shares of MPC common stock as stock consideration in the merger, former Andeavor stockholders may seek to sell the shares of MPC common stock delivered to them. Other MPC stockholders may also seek to sell shares of MPC common stock held by them following, or in anticipation of, completion of the merger. These sales (or the perception that these sales may occur), coupled with the increase in the outstanding number of shares of MPC common stock, may affect the market for, and the market price of, MPC common stock in an adverse manner.

The combined company will record goodwill and other intangible assets that could become impaired and result in material non-cash charges to the results of operations of the combined company in the future.

The merger will be accounted for as an acquisition by MPC in accordance with accounting principles generally accepted in the United States. Under the acquisition method of accounting, the assets and liabilities of Andeavor and its subsidiaries will be recorded, as of completion, at their respective fair values and added to those of MPC. The reported financial condition and results of operations of MPC for periods after completion of the

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merger will reflect Andeavor balances and results after completion of the merger, but will not be restated retroactively to reflect the historical financial position or results of operations of Andeavor and its subsidiaries for periods prior to the merger. See the section entitled “Unaudited Pro Forma Condensed Consolidated Combined Financial Statements” beginning on page 190.

Under the acquisition method of accounting, the total purchase price will be allocated to Andeavor’s tangible assets and liabilities and identifiable intangible assets based on their fair values as of the date of completion of the merger. The excess of the purchase price over those fair values will be recorded as goodwill. MPC and Andeavor expect that the merger will result in the creation of goodwill based upon the application of the acquisition method of accounting. To the extent the value of goodwill or intangibles becomes impaired, the combined company may be required to incur material non-cash charges relating to such impairment. The combined company’s operating results may be significantly impacted from both the impairment and the underlying trends in the business that triggered the impairment.

Risks Relating to MPC’s Business

You should read and consider risk factors specific to MPC’s businesses that will also affect the combined company after the completion of the merger. These risks are described in Part I, Item 1A of MPC’s Annual Report on Form 10-K for the year ended December 31, 2017, and in other documents that are incorporated by reference herein. See the section entitled “Where You Can Find More Information” beginning on page 234 for the location of information incorporated by reference in this joint proxy statement/prospectus.

Risks Relating to Andeavor’s Business

You should read and consider risk factors specific to Andeavor’s businesses that will also affect the combined company after the completion of the merger. These risks are described in Part I, Item 1A of Andeavor’s Annual Report on Form 10-K for the year ended December 31, 2017, and in other documents that are incorporated by reference herein. See the section entitled “Where You Can Find More Information” beginning on page 234 for the location of information incorporated by reference in this joint proxy statement/prospectus.

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INFORMATION ABOUT THE COMPANIES

Marathon Petroleum Corporation

539 South Main Street

Findlay, OH 45840

Phone: 419-422-2121

MPC was incorporated in Delaware on November 9, 2009 in connection with an internal restructuring of Marathon Oil Corporation. Based in Findlay, Ohio, MPC is the nation’s second-largest refiner, with a crude oil refining capacity of approximately 1.9 million barrels per calendar day in its six-refinery system. Marathon brand gasoline is sold through approximately 5,600 independently owned retail outlets across 20 states and the District of Columbia. In addition, Speedway LLC, an MPC subsidiary, owns and operates the nation’s second-largest convenience store chain, with approximately 2,740 convenience stores in 21 states. MPC owns, leases or has ownership interests in approximately 10,800 miles of crude oil and light product pipelines. Through subsidiaries, MPC owns the general partner of MPLX LP, a midstream master limited partnership, which is referred to as MPLX. Through MPLX, MPC has ownership interests in gathering and processing facilities with approximately 5.9 billion cubic feet per day of gathering capacity, 8.4 billion cubic feet per day of natural gas processing capacity and 610,000 barrels per day of fractionation capacity, and is one of the largest natural gas processors in the United States and the largest processor and fractionator in the Marcellus and Utica shale regions. MPC’s fully integrated system provides operational flexibility to move crude oil, NGLs, feedstocks and petroleum-related products efficiently through the company’s distribution network and midstream service businesses in the Midwest, Northeast, East Coast, Southeast and Gulf Coast regions. MPC owns 100% of the outstanding equity interests of MPLX GP LLC, the general partner of MPLX. Additionally, as of March 31, 2018, MPC owned approximately 63.6% of the outstanding common units of MPLX.

Andeavor

19100 Ridgewood Parkway

San Antonio, TX 78259

Phone: 210-626-6000

Andeavor, whose legal name is Andeavor, changed its name on August 1, 2017 from Tesoro Corporation. Andeavor was incorporated in Delaware in 1968. Headquartered in San Antonio, Texas, Andeavor is a highly integrated marketing, logistics and refining company operating primarily in the western and mid-continent United States. Andeavor’s marketing segment sells gasoline and diesel fuel in the western and mid-continent United States through retail, branded and unbranded channels along with convenience store products in its retail channel. The retail and branded businesses primarily use the ARCO^®, Shell^®, Mobil^® and SUPERAMERICA^® brands for fuel sales and ampm^®, SUPERAMERICA^® and Giant^® brands for convenience stores. Andeavor’s logistics segment includes the operations of Andeavor Logistics LP, a master limited partnership which we refer to as Andeavor Logistics, with the exception of the wholesale fuel business acquired as part of Andeavor’s merger with Western Refining. Andeavor Logistics owns and operates crude oil and refined products logistics assets in the United States. Andeavor’s refining segment buys and refines crude oil and other feedstocks into transportation fuels that it sells to a wide variety of customers. Andeavor owns 100% of the outstanding equity interest of Tesoro Logistics GP, LLC, the general partner of Andeavor Logistics. Additionally, as of March 31, 2018, Andeavor owned approximately 59% of the outstanding common units of Andeavor Logistics.

Mahi Inc.

c/o Marathon Petroleum Corporation

539 South Main Street

Findlay, OH 45840

Phone: 419-422-2121

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Merger Sub 1, whose legal name is Mahi Inc., is a direct, wholly owned subsidiary of MPC. Upon the completion of the first merger, Merger Sub 1 will cease to exist. Merger Sub 1 was incorporated in Delaware on April 27, 2018 for the sole purpose of effecting the first merger.

Mahi LLC

c/o Marathon Petroleum Corporation

539 South Main Street

Findlay, OH 45840

Phone: 419-422-2121

Merger Sub 2, whose legal name is Mahi LLC, is a direct, wholly owned subsidiary of MPC. Upon the completion of the second merger, Merger Sub 2 will survive the second merger and continue to exist as a direct, wholly owned subsidiary of MPC. Merger Sub 2 was formed in Delaware on April 27, 2018 for the sole purpose of effecting the second merger.

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SPECIAL MEETING OF MPC STOCKHOLDERS

Date, Time and Place

The MPC special meeting will be held at [            ] Eastern Time on [            ], 2018, in the Auditorium of Marathon Petroleum Corporation, 539 South Main Street, Findlay, Ohio 45840.

Purpose of the MPC Special Meeting

The purpose of the MPC special meeting is as follows:

MPC will transact no other business at the MPC special meeting.

Recommendation of the MPC Board

The MPC board recommends that MPC stockholders vote:

See the section entitled “The Merger—Recommendation of the MPC Board and Reasons for the Merger” beginning on page 89.

Record Date

Only holders of record of issued and outstanding shares of MPC common stock as of the close of business on [            ], 2018, the record date for the MPC special meeting, are entitled to notice of, and to vote at, the MPC special meeting or any adjournment or postponement of the MPC special meeting.

Quorum; Required Votes; Abstentions and Broker Non-Votes

A quorum of MPC stockholders is necessary to hold a valid meeting. A quorum will exist at the MPC special meeting with respect to each matter to be considered at the MPC special meeting if the holders of a majority of shares of MPC common stock outstanding and entitled to vote on the record date are present in person or represented by proxy at the MPC special meeting. All shares represented by proxy are counted as present for purposes of establishing a quorum, including abstentions. Under the NYSE rules, brokers who hold shares in “street name” for a beneficial owner of those shares typically have the authority to vote in their discretion on “routine” proposals when they have not received instructions from beneficial owners. However, brokers are not allowed to exercise their voting discretion with respect to the approval of proposals that the NYSE determines to be “non-routine” and will not vote on such proposals if the broker has not received instructions from the beneficial owners on how to vote on the proposals. Under the NYSE rules, brokers are not permitted to vote on any of the matters to be considered at the MPC special meeting. As a result, your shares will not be voted on any matter unless you affirmatively instruct your bank, broker or other nominee how to vote your shares in one of the ways indicated by your bank, broker or other nominee.

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If you submit a properly executed proxy card, even if you do not vote for some or all of the proposals or vote to “ABSTAIN” in respect of some or all of the proposals, your shares of MPC common stock will be counted for purposes of calculating whether a quorum is present at the MPC special meeting with respect to each matter to be considered at the MPC special meeting. Executed but unvoted proxies will be voted in accordance with the recommendations of the MPC board. If additional votes must be solicited to approve the MPC issuance proposal, it is expected that the MPC special meeting will be adjourned to solicit additional proxies. Shares of MPC common stock held in street name will be counted as present for the purpose of determining the existence of a quorum at the MPC special meeting so long as a stockholder has given the bank, broker or other nominee voting instructions on at least one of the proposals brought before the MPC special meeting. The proposals for consideration at the MPC special meeting are considered “non-routine” matters under NYSE Rule 452, and, therefore, no broker non-votes can occur at the meeting. A stockholder’s shares will not be counted as present for the purpose of determining the existence of a quorum if no instructions have been provided on how to vote on any such proposals.

Approval of the MPC issuance proposal requires the affirmative vote of a majority of votes cast by MPC stockholders present in person or by proxy at the MPC special meeting and entitled to vote on the proposal. Under the NYSE rules, abstentions will have the same effect as a vote “AGAINST” the proposal.

Approval of the MPC authorized stock COI amendment proposal requires the affirmative vote of a majority of the shares of MPC common stock outstanding as of the close of business on the record date and entitled to vote on the proposal. Abstentions will have the same effect as a vote “AGAINST” the proposal.

Approval of the MPC board size COI amendment proposal requires the affirmative vote of at least 80% of the shares of MPC common stock outstanding as of the close of business on the record date and entitled to vote on the proposal. Abstentions will have the same effect as a vote “AGAINST” the proposal.

Approval of the MPC adjournment proposal requires the affirmative vote of a majority of shares held by MPC stockholders present in person or by proxy at the MPC special meeting and entitled to vote on the proposal. Abstentions will have the same effect as a vote “AGAINST” the proposal.

The matters to be voted on at the MPC special meeting are described in the section entitled “MPC Proposals” beginning on page 68.

Methods of Voting

If your shares of MPC common stock are registered in your name with MPC’s transfer agent, Computershare Investor Services, LLC, you are a stockholder of record with respect to those shares and you received printed proxy materials directly from us. If your shares are held in an account at a bank, broker or other similar organization, you are the “beneficial owner” of such shares and the printed proxy materials were forwarded to you by that organization. In that circumstance, the organization is considered the stockholder of record for purposes of voting at the MPC special meeting. As a beneficial owner, you have the right to instruct the organization how to vote the shares held in your account.

If you are a stockholder of record of MPC common stock, you may vote:

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If you are a beneficial owner of shares of MPC common stock held in street name, you may vote:

We provide Internet proxy voting to allow you to vote your shares online; however, please be aware you must bear any costs associated with your Internet access, such as usage charges from Internet access providers or telecommunication companies.

Voting in Person

Owners of record will need to have a valid form of government-issued photo identification to be admitted to the MPC special meeting. If your ownership is through a bank, broker or other nominee, then, in addition to a valid form of government-issued photo identification, you will also need to have proof of your share ownership to be admitted to the MPC special meeting. A recent account statement, letter or proxy from your bank, broker or other nominee will suffice. In order to vote at the MPC special meeting, if you are not an owner of record, you must first obtain a legal proxy form from the bank, broker or other nominee that holds your shares. Even if you plan to attend the MPC special meeting, the MPC board recommends that you vote your shares in advance as described below so that your vote will be counted if you later decide not to attend the MPC special meeting.

Voting by Proxy

Whether you hold your shares directly as the stockholder of record or beneficially in “street name,” you may direct your vote by proxy without attending the MPC special meeting. You can vote by proxy via the Internet, by telephone or by mail by following the instructions provided in the enclosed proxy card.

Questions About Voting

If you have any questions about how to vote or direct a vote in respect of your shares of MPC common stock, you may contact Innisfree, MPC’s proxy solicitor, at:

Revocability of Proxies

If you are a stockholder of record of MPC, you may change your vote or revoke your proxy at any time before your shares are voted at the MPC special meeting by:

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If you are a beneficial owner of shares of MPC common stock, you must contact your bank, broker or other nominee with whom you have an account to obtain information regarding changing your voting instructions.

Proxy Solicitation Costs

The enclosed proxy card is being solicited on behalf of the MPC board. In addition to solicitation by mail, MPC’s directors, officers and employees may solicit proxies in person, by telephone or by electronic means. These persons will not be specifically compensated for doing this.

MPC has retained Innisfree to assist in the solicitation process. MPC will pay Innisfree a fee of approximately $25,000 as well as reasonable and documented out-of-pocket expenses. MPC also has agreed to indemnify Innisfree against various liabilities and expenses that relate to or arise out of its solicitation of proxies (subject to certain exceptions).

MPC will ask banks, brokers and other custodians, nominees and fiduciaries to forward the proxy solicitation materials to the beneficial owners of shares of MPC common stock held of record by such nominee holders. MPC will reimburse these nominee holders for their customary clerical and mailing expenses incurred in forwarding the proxy solicitation materials to the beneficial owners.

No Dissenters’ Rights

Under Delaware law, MPC stockholders are not entitled to appraisal rights in connection with the issuance of shares of MPC common stock as contemplated by the merger agreement.

Other Information

The matters to be considered at the MPC special meeting are of great importance to the stockholders of MPC. Accordingly, you are urged to read and carefully consider the information contained in or incorporated by reference into this joint proxy statement/prospectus and submit your proxy via the Internet or by telephone or complete, date, sign and promptly return the enclosed proxy card in the enclosed postage-paid envelope. If you submit your proxy via the Internet or by telephone, you do not need to return the enclosed proxy card.

Vote of MPC’s Directors and Executive Officers

As of June 29, 2018, MPC directors and executive officers, and their affiliates, as a group, owned and were entitled to vote 1,101,269 shares of MPC common stock, or less than 1% of the total outstanding shares of MPC common stock as of June 29, 2018. This is less than the number of shares of MPC common stock beneficially owned by such persons as some forms of beneficial ownership do not confer voting rights.

MPC currently expects that all of its directors and executive officers will vote their shares “FOR” the MPC issuance proposal, “FOR” the MPC authorized stock COI amendment proposal, “FOR” the MPC board size COI amendment proposal and “FOR” the MPC adjournment proposal.

Attending the MPC Special Meeting

You are entitled to attend the MPC special meeting only if you were a stockholder of record of MPC at the close of business on the record date or you held your shares of MPC beneficially in the name of a bank, broker or other nominee as of the record date, or you hold a valid proxy for the MPC special meeting.

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If you were a stockholder of record of MPC at the close of business on the record date and wish to attend the MPC special meeting, please so indicate on the appropriate proxy card or as prompted by the Internet or telephone voting system. Your name will be verified against the list of stockholders of record prior to your being admitted to the MPC special meeting.

If a bank, broker or other nominee is the record owner of your shares of MPC common stock, you will need to have proof that you are the beneficial owner as of the record date to be admitted to the MPC special meeting. A recent statement or letter from your bank, broker or other nominee confirming your ownership as of the record date, or presentation of a valid proxy from a bank, broker or other nominee that is the record owner of your shares, would be acceptable proof of your beneficial ownership.

You should be prepared to present government-issued photo identification for admittance to the MPC special meeting. If you do not provide government-issued photo identification or comply with the other procedures outlined above upon request, you might not be admitted to the MPC special meeting.

Results of the MPC Special Meeting

The preliminary voting results will be announced at the MPC special meeting. In addition, within four business days following the MPC special meeting, MPC intends to file the final voting results with the SEC on a Current Report on Form 8-K. If the final voting results have not been certified within that four business day period, MPC will report the preliminary voting results on a Current Report on Form 8-K at that time and will file an amendment to the Current Report on Form 8-K to report the final voting results within four business days of the date that the final results are certified.

MPC STOCKHOLDERS SHOULD CAREFULLY READ THIS JOINT PROXY STATEMENT/PROSPECTUS IN ITS ENTIRETY FOR MORE DETAILED INFORMATION CONCERNING THE MPC ISSUANCE PROPOSAL AND THE OTHER MATTERS TO BE VOTED ON AT THE MPC SPECIAL MEETING.

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MPC PROPOSALS

MPC Issuance Proposal

It is a condition to completion of the merger that MPC stockholders approve the issuance of shares of MPC common stock in the merger. In the merger, each Andeavor stockholder will receive, for each share of Andeavor common stock that is issued and outstanding as of immediately prior to the effective time of the first merger, either the cash consideration of $152.27, if the Andeavor stockholder makes a cash election with respect to such share, or the stock consideration of 1.87 shares of MPC common stock, if the Andeavor stockholder makes or is deemed to have made a stock election with respect to such share. The cash and stock elections are subject to the allocation and proration procedures set forth in the merger agreement, which are described in the section entitled “The Merger Agreement—Merger Consideration” beginning on page 153.

Under the NYSE rules, a company is required to obtain stockholder approval prior to the issuance of shares of common stock if the number of shares of common stock to be issued is, or will be upon issuance, equal to or in excess of 20% of the number of shares of common stock outstanding before the issuance of the common stock. If the merger is completed pursuant to the merger agreement, MPC expects to issue up to approximately 240 million shares of MPC common stock in connection with the merger, depending upon the number of shares of Andeavor common stock (other than excluded shares) outstanding as of the effective time of the first merger. Accordingly, the aggregate number of shares of MPC common stock that MPC will issue in the merger will exceed 20% of the shares of MPC common stock outstanding before such issuance, and for this reason, MPC is seeking the approval of MPC stockholders for the issuance of shares of MPC common stock pursuant to the merger agreement. In the event the MPC issuance proposal is not approved by MPC stockholders, the merger cannot be completed.

In the event the MPC issuance proposal is approved by MPC stockholders, but the merger agreement is terminated (without the merger being completed) prior to the issuance of shares of MPC common stock pursuant to the merger agreement, MPC will not issue any shares of MPC common stock as a result of the approval of the MPC issuance proposal.

Approval of the MPC issuance proposal requires the affirmative vote of a majority of votes cast by stockholders present in person or by proxy at the MPC special meeting and entitled to vote on the proposal. Under the NYSE rules, abstentions will have the same effect as a vote “AGAINST” this proposal.

The MPC board recommends you vote “FOR” the MPC issuance proposal.

MPC Authorized Stock COI Amendment Proposal

The MPC certificate of incorporation provides that the total number of shares of common stock which MPC will have the authority to issue is one billion. MPC is seeking to amend its certificate of incorporation prior to the merger in order to increase the authorized number of shares of MPC common stock from one billion shares to two billion shares. The MPC authorized stock COI amendment is contingent upon completion of the merger.

MPC has a sufficient number of authorized but unissued shares, and shares held in treasury, under its current certificate of incorporation to complete the merger, and completion of the merger is not conditioned upon approval of the MPC authorized stock COI amendment proposal. However, completion of the merger will reduce the number of remaining authorized but unissued shares available to MPC in the future. After completion of the merger, MPC estimates that it would have approximately 696 million shares of common stock outstanding and, after giving effect to approximately 93 million shares of common stock reserved for issuance, would have only, in the aggregate, approximately 211 million shares of common stock authorized but unissued and shares held in treasury available for future issuance. The MPC board believes that the increased number of authorized shares of MPC common stock contemplated by the proposed amendment is important to the combined company in order

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that additional shares be available for issuance from time to time, without further action or authorization by the MPC stockholders (except as required by law or the NYSE rules), if needed for such corporate purposes as may be determined by the MPC board. Such corporate purposes might include the acquisition of other businesses in exchange for shares of MPC common stock; facilitating broader ownership of MPC common stock by effecting stock splits or issuing a stock dividend; flexibility for possible future financings; and attracting and retaining valuable employees and directors by the issuance of additional stock-based awards. The MPC board considers the authorization of additional shares advisable to ensure prompt availability of shares for issuance should the occasion arise. The additional one billion shares authorized would be a part of the existing class of MPC common stock and, if issued, would have the same rights and privileges as the shares of MPC common stock presently issued and outstanding.

Approval of the MPC authorized stock COI amendment proposal requires the affirmative vote of a majority of the shares of MPC common stock outstanding as of the record date and entitled to vote. Abstentions will have the same effect as a vote “AGAINST” the proposal.

The MPC board recommends you vote “FOR” the MPC authorized stock COI amendment proposal.

MPC Board Size COI Amendment Proposal

The MPC certificate of incorporation provides that the maximum number of directors permitted to serve on the MPC board is 12. The merger agreement provides that promptly after the effective time of the first merger, MPC will cause the maximum number of directors on the MPC board to be increased from 12 to 14, and MPC will cause four current members of the Andeavor board to be appointed to the MPC board in director classes to be agreed by MPC and Andeavor. The merger agreement obligates MPC to use its reasonable best efforts to cause such four individuals to be elected to the MPC board in accordance with the MPC certificate of incorporation or the MPC bylaws at the first annual meeting of stockholders of MPC at which such director is eligible for election.

In order to satisfy MPC’s obligations under the merger agreement and to provide for additional board seats for possible future growth, MPC is seeking to amend its certificate of incorporation prior to the merger in order to allow up to 14 directors. The MPC board size COI amendment is contingent upon completion of the merger. Should the MPC board size COI amendment proposal not be approved, two directors of MPC’s current board will resign in order to appoint the four Andeavor appointees.

Approval of the MPC board size COI amendment proposal requires the affirmative vote of at least 80% of the shares of MPC common stock outstanding as of the record date and entitled to vote. Abstentions will have the same effect as a vote “AGAINST” the proposal.

The MPC board recommends you vote “FOR” the MPC board size COI amendment proposal

MPC Adjournment Proposal

MPC stockholders are also being asked to approve a proposal to adjourn the MPC special meeting, if reasonably necessary, to provide stockholders with any required supplement or amendment to the accompanying joint proxy statement/prospectus or to solicit additional proxies in favor of the MPC issuance proposal in the event there are not sufficient votes at the time of the MPC special meeting to approve the MPC issuance proposal. If the MPC special meeting is adjourned for the purpose of soliciting additional proxies, stockholders who have already submitted their proxies will be able to revoke them at any time prior to their exercise.

Approval of the MPC adjournment proposal requires the affirmative vote of a majority of shares held by MPC stockholders present in person or by proxy at the MPC special meeting and entitled to vote on the proposal, regardless of whether a quorum is present. Abstentions will have the same effect as a vote “AGAINST” the proposal.

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Approval of the MPC adjournment proposal is not required in order for the MPC special meeting to be adjourned. Under the MPC bylaws, the presiding person of the MPC special meeting has the power to adjourn or recess the MPC special meeting from time to time whether or not a quorum is present.

The MPC board recommends you vote “FOR” the MPC adjournment proposal.

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SPECIAL MEETING OF ANDEAVOR STOCKHOLDERS

Date, Time and Place

The Andeavor special meeting will be held on [            ], 2018, at [            ] Central Time at 19100 Ridgewood Parkway, San Antonio, Texas 78259.

Purpose of the Andeavor Special Meeting

The purpose of the Andeavor special meeting is as follows:

Andeavor will transact no other business at the Andeavor special meeting.

Recommendation of the Andeavor Board of Directors

The Andeavor board recommends that Andeavor stockholders vote:

See the section entitled “The Merger—Recommendation of the Andeavor Board and Reasons for the Merger” beginning on page 118.

Record Date

Only holders of record of issued and outstanding shares of Andeavor common stock as of the close of business on [            ], 2018 the record date for the Andeavor special meeting, are entitled to notice of, and to vote at, the Andeavor special meeting or any adjournment or postponement of the Andeavor special meeting.

Quorum; Required Votes; Abstentions and Broker Non-Votes

A quorum of Andeavor stockholders is necessary to hold a valid meeting. A quorum will exist at the Andeavor special meeting with respect to each matter to be considered at the Andeavor special meeting if the holders of a majority of shares of Andeavor common stock outstanding and entitled to vote on the record date are present in person or represented by proxy at the Andeavor special meeting. All shares represented by proxy are counted as present for purposes of establishing a quorum, including abstentions. Under the NYSE rules, brokers who hold shares in “street name” for a beneficial owner of those shares typically have the authority to vote in their discretion on “routine” proposals when they have not received instructions from beneficial owners. However, brokers are not allowed to exercise their voting discretion with respect to the approval of proposals that the NYSE determines to be “non-routine” and will not vote on such proposals if the broker has not received instructions from the beneficial owners on how to vote on the proposals. Under the NYSE rules, brokers are not permitted to vote on any of the matters to be considered at the Andeavor special meeting. As a result, your shares will not be voted on any matter unless you affirmatively instruct your bank, broker or other nominee how to vote your shares in one of the ways indicated by your bank, broker or other nominee.

If you submit a properly executed proxy card, even if you do not vote for some or all of the proposals or vote to “ABSTAIN” in respect of some or all of the proposals, your shares of Andeavor common stock will be

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counted for purposes of calculating whether a quorum is present at the Andeavor special meeting with respect to each matter to be considered at the Andeavor special meeting. Executed but unvoted proxies will be voted in accordance with the recommendations of the Andeavor board. If additional votes must be solicited to approve the Andeavor merger proposal, it is expected that the meeting will be adjourned to solicit additional proxies. Shares of Andeavor common stock held in street name will be counted as present for the purpose of determining the existence of a quorum at the Andeavor special meeting so long as a stockholder has given the broker or other nominee voting instructions on at least one of the proposals brought before the Andeavor special meeting. The proposals for consideration at the Andeavor special meeting are considered “non-routine” matters under NYSE Rule 452, and, therefore, no broker non-votes can occur at the meeting. A stockholder’s shares will not be counted as present for the purpose of determining the existence of a quorum if no instructions have been provided on how to vote on any such proposals.

Approval of the Andeavor merger proposal requires the affirmative vote of a majority of the shares of Andeavor common stock outstanding as of the close of business on the record date and entitled to vote on the proposal. Abstentions will have the same effect as a vote “AGAINST” the proposal.

Approval of the Andeavor compensation proposal requires the affirmative vote of a majority of the shares of Andeavor common stock present in person or by proxy at the Andeavor special meeting and entitled to vote on the proposal. Abstentions will have the same effect as a vote “AGAINST” the proposal.

Approval of the Andeavor adjournment proposal requires the affirmative vote of a majority of the shares of Andeavor common stock present in person or by proxy at the Andeavor special meeting and entitled to vote on the proposal. Abstentions will have the same effect as a vote “AGAINST” the proposal.

The matters to be voted on at the Andeavor special meeting are described in the section entitled “Andeavor Proposals” beginning on page 76.

Methods of Voting

Andeavor stockholders holding shares directly as stockholders of record may vote via the Internet by going to the web address provided on the enclosed proxy card and following the instructions for Internet voting; by telephone using the toll-free telephone number listed on the enclosed proxy card; or by completing, signing, dating and returning the enclosed proxy card in the postage-paid envelope provided.

Andeavor stockholders of record may vote their shares (other than shares held in the Andeavor 401(k) Plan) in person by ballot at the Andeavor special meeting or by submitting their proxies:

If your shares are held in the Andeavor 401(k) Plan, you may not vote in person at the Andeavor special meeting. Instead you will need to vote by submitting your proxy:

Stockholders of Andeavor whose shares are held in “street name” by a broker, nominee, fiduciary or other custodian should refer to the proxy card, voting instruction form or other information forwarded by their broker, nominee, fiduciary or other custodian for instructions on how to vote their shares.

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Voting in Person

Shares held directly in your name as stockholder of record may be voted in person at the Andeavor special meeting. If you choose to vote your shares in person at the Andeavor special meeting, please bring your enclosed proxy card and government-issued photo identification. Even if you plan to attend the Andeavor special meeting, the Andeavor board recommends that you vote your shares in advance as described below so that your vote will be counted if you later decide not to attend the Andeavor special meeting. Please note that if your shares are held in the Andeavor 401(k) Plan, you may not vote in person at the Andeavor special meeting, instead you will need to submit your vote through one of the ways described above.

If you are a beneficial holder of your shares of Andeavor stock, you will receive separate voting instructions from your broker, bank or other nominee explaining how to vote your shares. Please note that if your shares are held in “street name” by a broker, bank or other nominee and you wish to vote at the Andeavor special meeting, you will not be permitted to vote in person unless you first obtain a legal proxy issued in your name from the record owner. You are encouraged to request a legal proxy from your broker, bank or other nominee promptly as the process can be lengthy.

Voting by Proxy

If you hold your shares of Andeavor common stock directly as the stockholder of record you may direct your vote by proxy without attending the Andeavor special meeting. You can vote by proxy via the Internet, by telephone or by mail by following the instructions provided in the enclosed proxy card.

Stockholders of Andeavor whose shares are held in “street name” by a broker, nominee, fiduciary or other custodian should refer to the proxy card, voting instruction form or other information forwarded by their broker, nominee, fiduciary or other custodian for instructions on how to vote their shares.

Questions About Voting

If you have any questions about how to vote or direct a vote in respect of your shares of Andeavor common stock, you may contact Innisfree, Andeavor’s proxy solicitor, at:

Stockholders may call toll-free at 1-888-750-5834.

Banks and brokers may call collect at 1-212-750-5833.

Revocability of Proxies

If you are a stockholder of record of Andeavor, whether you vote via the Internet, by telephone or mail, you can change or revoke your proxy before it is voted at the Andeavor special meeting in one of the following ways:

Proxy Solicitation Costs

The enclosed proxy card is being solicited on behalf of the Andeavor board. In addition to solicitation by mail, Andeavor’s directors, officers and employees may solicit proxies in person, by telephone or by electronic means. These persons will not be specifically compensated for doing this.

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Andeavor has retained Innisfree to assist in the solicitation process. Andeavor will pay Innisfree a fee of approximately $25,000, as well as reasonable and documented out-of-pocket expenses. Andeavor also has agreed to indemnify Innisfree against various liabilities and expenses that relate to or arise out of its solicitation of proxies (subject to certain exceptions).

Andeavor will ask banks, brokers and other custodians, nominees and fiduciaries to forward the proxy solicitation materials to the beneficial owners of shares of Andeavor common stock held of record by such nominee holders. Andeavor will reimburse these nominee holders for their customary clerical and mailing expenses incurred in forwarding the proxy solicitation materials to the beneficial owners.

Other Information

The matters to be considered at the Andeavor special meeting are of great importance to the stockholders of Andeavor. Accordingly, you are urged to read and carefully consider the information contained in or incorporated by reference into this joint proxy statement/prospectus and submit your proxy via the Internet or by telephone or complete, date, sign and promptly return the enclosed proxy card in the enclosed postage-paid envelope. If you submit your proxy via the Internet or by telephone, you do not need to return the enclosed proxy card.

Vote of Andeavor’s Directors and Executive Officers

As of June 29, 2018, Andeavor directors and executive officers, and their affiliates, as a group, were entitled to vote or had shared power to vote a total of 9,260,540 shares of Andeavor common stock, or approximately 6.1% of the total shares of Andeavor common stock issued and outstanding as of June 29, 2018. One such director, Paul L. Foster, has entered into a separate voting agreement with MPC, Andeavor, Merger Sub 1, Merger Sub 2 and Franklin Mountain Investments, LP pursuant to which he has agreed, among other things, to vote all of the shares of Andeavor common stock beneficially owned by him (constituting approximately 5.2% of the total shares of Andeavor stock issued and outstanding as of April 26, 2018), other than those shares sold pursuant to his current 10b5-1 trading plan, in favor of the adoption of the merger agreement, on the terms and subject to the conditions set forth in the voting agreement. For more information, see the section entitled “Voting and Support Agreement” beginning on page 184.

Andeavor currently expects that all of its directors and executive officers will vote their shares “FOR” the Andeavor merger proposal, “FOR” the Andeavor compensation proposal and “FOR” the Andeavor adjournment proposal.

Attending the Andeavor Special Meeting

You are entitled to attend the Andeavor special meeting only if you were a stockholder of record of Andeavor at the close of business on the record date or you held your shares of Andeavor beneficially in the name of a broker, bank or other nominee as of the record date or you hold a valid proxy for the Andeavor special meeting.

If you were a stockholder of record of Andeavor at the close of business on the record date and wish to attend the Andeavor special meeting, please so indicate on the appropriate proxy card or as prompted by the Internet or telephone voting system. Your name will be verified against the list of Andeavor stockholders of record prior to your being admitted to the Andeavor special meeting.

If a broker, bank or other nominee is the record owner of your shares of Andeavor common stock, you will need to have proof that you are the beneficial owner as of the record date to be admitted to the Andeavor special meeting. A recent statement or letter from your broker, bank or other nominee confirming your ownership as of the record date, or presentation of a valid proxy from a broker, bank or other nominee that is the record owner of your shares, would be acceptable proof of your beneficial ownership.

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You should be prepared to present government-issued photo identification for admittance to the Andeavor special meeting. If you do not provide government-issued photo identification or comply with the other procedures outlined above upon request, you might not be admitted to the Andeavor special meeting.

Results of the Andeavor Special Meeting

The preliminary voting results will be announced at the Andeavor special meeting. In addition, within four business days following the Andeavor special meeting, Andeavor intends to file the final voting results with the SEC on a Current Report on Form 8-K. If the final voting results have not been certified within that four business day period, Andeavor will report the preliminary voting results on a Current Report on Form 8-K at that time and will file an amendment to the Current Report on Form 8-K to report the final voting results within four business days of the date that the final results are certified.

ANDEAVOR STOCKHOLDERS SHOULD CAREFULLY READ THIS JOINT PROXY STATEMENT/PROSPECTUS IN ITS ENTIRETY FOR MORE DETAILED INFORMATION CONCERNING THE ANDEAVOR MERGER PROPOSAL AND THE OTHER MATTERS TO BE VOTED ON AT THE ANDEAVOR SPECIAL MEETING.

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ANDEAVOR PROPOSALS

Merger Proposal

It is a condition to the completion of the merger that Andeavor stockholders adopt the merger agreement. In the merger, each Andeavor stockholder will receive, for each share of Andeavor common stock that is issued and outstanding as of immediately prior to the effective time of the first merger, either the cash consideration of $152.27, if the Andeavor stockholder makes a cash election with respect to such share, or the stock consideration of 1.87 shares of MPC common stock, if the Andeavor stockholder makes or is deemed to have made a stock election with respect to such share. The cash and stock elections are subject to the allocation and proration procedures set forth in the merger agreement, which are described in the section entitled “The Merger Agreement—Merger Consideration” beginning on page 153.

The approval by such stockholders of this proposal is required by Section 251 of the DGCL and is a condition to the completion of the merger.

Approval of the Andeavor merger proposal requires the affirmative vote of a majority of the shares of Andeavor common stock outstanding as of the close of business on the record date and entitled to vote. Abstentions will have the same effect as a vote “AGAINST” the proposal.

The Andeavor board recommends that you vote “FOR” the Andeavor merger proposal.

Andeavor Compensation Proposal

As required by Section 14A of the Exchange Act and the applicable SEC rules issued thereunder, which were enacted pursuant to the Dodd-Frank Wall Street Reform and Consumer Protection Act, Andeavor is required to provide its stockholders the opportunity to vote to approve, on a non-binding, advisory basis, certain compensation that may be paid or become payable to Andeavor’s named executive officers that is based on or otherwise relates to the merger, as described in the section entitled “The Merger—Interests of Andeavor Directors and Executive Officers in the Merger” beginning on page 144. Accordingly, Andeavor stockholders are being provided the opportunity to cast an advisory vote on such potential payments.

As an advisory vote, this proposal is not binding upon Andeavor or the Andeavor board and approval of this proposal is not a condition to the completion of the merger. Because the merger-related executive compensation to be paid in connection with the merger is based on the terms of the merger agreement as well as the contractual arrangements with Andeavor’s named executive officers, such compensation will be payable, regardless of the outcome of this advisory vote, if the merger agreement is adopted (subject only to the contractual conditions applicable thereto). However, Andeavor seeks the support of its stockholders and believes that stockholder support is appropriate because Andeavor has a comprehensive executive compensation program designed to link the compensation of its executives with Andeavor’s performance and the interests of Andeavor stockholders. Accordingly, holders of Andeavor common stock are being asked to vote on the following resolution:

“RESOLVED, that the stockholders of Andeavor approve, on an advisory, non-binding basis, certain compensation that may be paid or become payable to the named executive officers of Andeavor that is based on or otherwise relates to the merger, as disclosed pursuant to Item 402(t) of Regulation S-K under the heading “Interests of Andeavor Directors and Officers in the Merger.”

Approval of the non-binding compensation proposal requires the affirmative vote of a majority of the shares of Andeavor common stock present in person or by proxy at the Andeavor special meeting and entitled to vote on the proposal. Abstentions will have the same effect as a vote “AGAINST” the proposal.

The Andeavor board recommends that you vote “FOR” the Andeavor compensation proposal.

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Andeavor Adjournment Proposal

Andeavor stockholders are also being asked to approve a proposal to adjourn the Andeavor special meeting, if reasonably necessary, to provide stockholders with any required supplement or amendment to the accompanying joint proxy statement/prospectus or to solicit additional proxies in favor of the Andeavor merger proposal in the event there are not sufficient votes at the time of the Andeavor special meeting to approve the Andeavor merger proposal. If the Andeavor special meeting is adjourned for the purpose of soliciting additional proxies, stockholders who have already submitted their proxies will be able to revoke them at any time prior to their exercise.

Approval of the Andeavor adjournment proposal requires the affirmative vote of a majority of the shares of Andeavor common stock present in person or by proxy at the Andeavor special meeting and entitled to vote on the proposal, regardless of whether a quorum is present. Abstentions will have the same effect as a vote “AGAINST” the proposal.

The Andeavor board recommends that you vote “FOR” the Andeavor adjournment proposal.

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THE MERGER

This discussion of the merger is qualified in its entirety by reference to the merger agreement, which is attached to this joint proxy statement/prospectus as Annex A and incorporated by reference herein in its entirety. You should read the entire merger agreement carefully as it is the legal document that governs the merger.

Transaction Structure

At the effective time of the first merger, Merger Sub 1 will merge with and into Andeavor. As a result of the first merger, the separate corporate existence of Merger Sub 1 will cease, and Andeavor will continue as the surviving corporation and as a wholly owned subsidiary of MPC.

Immediately following the completion of the first merger, Andeavor will merge with and into Merger Sub 2 pursuant to the terms of the merger agreement. Upon the completion of the second merger, the separate corporate existence of Andeavor will cease as a result, and Merger Sub 2 will continue as the surviving company.

Consideration to Andeavor Stockholders

As a result of the merger, each share of Andeavor common stock issued and outstanding immediately prior to the first merger (other than excluded shares, as defined below, and Andeavor common stock that is issued and outstanding immediately prior to the effective time of the first merger and that is held by any person who is entitled to demand and properly demands appraisal of such Andeavor common stock pursuant to, and who complies in all respects with, Section 262 of the DGCL) will be converted into the right to receive either (i) the cash consideration of $152.27 or (ii) the stock consideration of 1.87 shares of MPC common stock, at the election of the holder of each such share of Andeavor common stock. An election to receive either the cash or stock consideration is subject to the allocation and proration procedures set forth in the merger agreement, which are described in the section entitled “The Merger Agreement—Merger Consideration” beginning on page 153. Andeavor stockholders who make no election or an untimely election, or are otherwise deemed not to have submitted an effective form of election, will be deemed to have elected to receive stock consideration.

Shares held by Andeavor, MPC or any of their respective direct or indirect subsidiaries (including Merger Sub 1 and Merger Sub 2) as of the effective time of the first merger, other than any shares of Andeavor common stock held on behalf of third parties, which are referred to as the excluded shares, will be cancelled and will cease to exist, and no cash, MPC stock or other consideration will be delivered in exchange therefor.

Andeavor stockholders who receive the stock consideration in respect of their shares of Andeavor common stock will not receive any fractional shares of MPC common stock in the merger. Instead, they will be entitled to receive, in lieu of such fractional shares, an amount in cash, without interest, equal to the product of the average of the closing prices per share of MPC common stock on the NYSE, as reported by The Wall Street Journal (or if not reported thereby, as reported in another authoritative source), for the five full trading days ending on the second business day immediately preceding the date on which the effective time occurs multiplied by the fraction of shares of MPC stock (after taking into account all of the shares of Andeavor common stock held by such holder at the effective time and rounded to the nearest one thousandth) to which such holder would otherwise be entitled.

The precise consideration that a Andeavor stockholder will receive will not be known at the time of the Andeavor special meeting or at the time that the election is made because it is dependent upon the aggregate number of shares of Andeavor common stock in respect of which elections to receive cash consideration and stock consideration are made.

Neither Andeavor nor MPC is making any recommendation as to whether an Andeavor stockholder should elect to receive the cash consideration or the stock consideration. If you are an Andeavor stockholder, you must make your own decision with respect to this election and you should seek the advice of your own attorneys, financial advisors and/or accountants.

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Background of the Merger

Andeavor and MPC are both independent refining, logistics, and marketing companies with their respective geographic footprints in the Western and Eastern regions of the United States. As part of their ongoing efforts to strengthen their respective businesses and enhance stockholder value, the boards of directors and senior management of each of Andeavor and MPC regularly review and assess their respective companies’ operations, performance, prospects and strategic directions, including the possibility of pursuing various strategic transactions. In connection with their ongoing efforts, the boards of directors of Andeavor and MPC have, at various board meetings, periodically reviewed the strategic landscape in their industry and evaluated various potential strategic opportunities for Andeavor and MPC, respectively. In considering these potential strategic opportunities, the boards of directors and senior management of Andeavor and MPC both have taken into account various factors, including potential synergy opportunities, geographic diversification, integration with logistics and marketing, asset quality and likelihood that such opportunity could be executed and be value enhancing for their respective stockholders. From time to time, the senior management of Andeavor and MPC have held conversations and communicated with various investment banking firms regarding potential strategic transaction opportunities and other strategic alternatives.

In March 2017, Mr. Gregory J. Goff, the Chairman, President and Chief Executive Officer of Andeavor, and Mr. Gary R. Heminger, the Chairman and Chief Executive Officer of MPC, met following an industry event and discussed various industry-related matters and, separately, the possibility of exploring a strategic transaction between the companies and the potential benefits of such a transaction given the similarity of the companies’ business models, the diversity of the geographic regions of their business operations and the possibility of potentially significant synergies from a strategic combination. Each of Messrs. Goff and Heminger stated that they needed to discuss the matter further with their respective boards and would follow-up with each other thereafter.

Beginning in April 2017, and from time to time thereafter, Goldman Sachs, Andeavor’s long-time financial advisor on potential strategic transactions provided to Andeavor certain publicly available financial data regarding a potential strategic combination with MPC at the request of Andeavor management.

In June 2017, Mr. Timothy T. Griffith, Senior Vice President and Chief Financial Officer of MPC, and Barclays discussed a potential engagement of Barclays as a financial advisor in connection with a potential transaction between MPC and Andeavor.

On June 27, 2017 and June 28, 2017, Messrs. Goff and Heminger met in person and again discussed the possibility of exploring a strategic transaction between the two companies, reiterating the same potential benefits of a strategic combination as they had discussed in March 2017.

In July 2017, Sullivan & Cromwell LLP, referred to as S&C, Andeavor’s long-time legal counsel in connection with potential strategic transactions, was updated with respect to the consideration of a potential strategic combination with MPC and asked to prepare a mutual confidentiality agreement. Also in July 2017, Goldman Sachs provided a draft disclosure letter regarding certain of its relationships with Andeavor, MPC, Andeavor Logistics and MPLX to Andeavor.

On July 26, 2017, the board of directors of MPC held a regularly scheduled meeting at which Mr. Heminger and other MPC executives provided a preliminary analysis regarding a possible strategic combination with Andeavor, which included the potential merits and other considerations associated with such a transaction. The information provided included Barclays’ disclosure regarding certain of its relationships with MPC, Andeavor and other relevant parties to the proposed transaction. The MPC board authorized continuing discussions with Andeavor in pursuit of such a transaction.

On July 28, 2017, the board of directors of Andeavor held a meeting to discuss a potential strategic transaction between MPC and Andeavor. During the meeting, Mr. Goff discussed with the board his conversation

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with Mr. Heminger regarding a potential strategic combination and presented to the board certain preliminary analyses of the opportunities and considerations presented by a strategic transaction with MPC, including the similarity of the companies’ business models, the diverse geographic regions of their refining operations and the possibility of potentially significant synergies from a strategic combination. The Andeavor board expressed its initial interest in exploring the possibility of a potential strategic combination with MPC and authorized Mr. Goff, Mr. Sterin, Executive Vice President and Chief Financial Officer of Andeavor, and Ms. Rucker, Executive Vice President, General Counsel and Secretary of Andeavor, to engage with MPC regarding the potential for such a transaction.

On July 29, 2017, Messrs. Goff and Heminger spoke by telephone to discuss exploring further a potential strategic combination between MPC and Andeavor. They agreed that the goal of the strategic transaction would be to create a leading integrated and geographically diverse refining, marketing and midstream company. Messrs. Goff and Heminger also discussed next steps, including entering into a confidentiality agreement and establishing a small team from each company to further explore the potential transaction.

In August 2017, Andeavor and MPC negotiated a mutual confidentiality agreement with customary rights and protections and mutual standstill provisions. Andeavor and MPC executed the confidentiality agreement on August 15, 2017, so they could begin to exchange certain preliminary non-public information to facilitate the evaluation, negotiation and implementation of a potential strategic combination between the two companies.

Late in the week of August 14, 2017, Messrs. Goff and Heminger met in person to further discuss the potential strategic transaction. They agreed to conduct a preliminary joint synergies assessment to evaluate the potential combination before engaging in further discussions. They also discussed the mechanics of preparing such preliminary synergies assessment and agreed to designate a limited number of subject matter experts from each company to work jointly on the assessment. On August 19, 2017, Ms. Rucker spoke with Ms. Suzanne Gagle, Vice President and General Counsel of MPC, by telephone to further discuss the legal parameters of the preliminary synergies assessment and it was agreed that the employees involved would sign confidentiality agreements.

On August 25, 2017, the MPC board held a telephonic meeting during which Mr. Heminger gave an update, noting that certain subject matter experts from both MPC and Andeavor would convene to undertake a synergies assessment the following week.