UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of

the Securities Exchange Act of 1934

Filed by the Registrant    ☒

Filed by a Party other than the Registrant    ☐

Check the appropriate box:

WESTERN GAS PARTNERS, LP

(Name of the Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

MERGER PROPOSAL—YOUR VOTE IS VERY IMPORTANT

January 28, 2019

Dear unitholders of Western Gas Partners, LP:

On November 7, 2018, Western Gas Equity Partners, LP (“WGP”), Western Gas Partners, LP (“WES”), Anadarko Petroleum Corporation (“APC”), WGR Asset Holding Company LLC (“WGRAH”) and certain of their affiliates entered into a Contribution Agreement and Agreement and Plan of Merger (as it may be amended from time to time, the “Merger Agreement”), pursuant to which, among other things, Clarity Merger Sub, LLC, a wholly owned subsidiary of WGP, will merge with and into WES, with WES continuing as the surviving entity and a subsidiary of WGP (the “Merger”). The board of directors (the “WES GP Board”) of Western Gas Holdings, LLC (“WES GP”), the general partner of WES, approved the Merger Agreement and the Merger and agreed to submit them to a vote of WES unitholders following the recommendation of the special committee of the WES GP Board (the “WES Special Committee”). The WES GP Board has unanimously, in good faith, determined that the Merger Agreement and the transactions contemplated thereby, including the Merger, are advisable, fair and reasonable to and in the best interests of WES and its limited partners, following the recommendation of the WES Special Committee that the Merger Agreement and the Merger are advisable, fair and reasonable to and in the best interests of WES and its limited partners (excluding WGP, APC and their respective affiliates) (the foregoing constituting “Special Approval” as defined in WES’s Second Amended and Restated Agreement of Limited Partnership, dated as of March 14, 2016, as heretofore amended (the “WES Partnership Agreement”)), and each of the WES GP Board and the WES Special Committee has approved the Merger Agreement and the transactions contemplated thereby, including the Merger. Under the terms of the Merger Agreement, subject to certain adjustments, each common unit representing a limited partner interest in WES (each a “WES common unit”) issued and outstanding immediately prior to the Merger (other than WES common units owned by WGP or subsidiaries of WGP or WES GP and 45,760,201 WES common units to be issued in the Contribution (as defined below)) will be converted into the right to receive 1.525 (the “exchange ratio”) common units representing limited partner interests in WGP (“WGP common units,” and the aggregate amount of such WGP common units, the “Merger Consideration”).

Immediately following the completion of the Merger, it is expected that WES unitholders (other than APC, WGP and their respective affiliates) will own approximately 33.8% of the outstanding WGP common units, based on the number of WGP common units outstanding, on a fully diluted basis, as of January 22, 2019. The common units of WGP and WES are traded on the New York Stock Exchange (“NYSE”) under the symbols “WGP” and “WES,” respectively.

Pursuant to the Merger Agreement, immediately prior to the Merger, (i) Anadarko E&P Onshore LLC and WGRAH will contribute all of their interests in each of Anadarko Wattenberg Oil Complex LLC, Anadarko DJ Oil Pipeline LLC, Anadarko DJ Gas Processing LLC, Wamsutter Pipeline LLC, DBM Oil Services, LLC, Anadarko Pecos Midstream LLC, Anadarko Mi Vida LLC and APC Water Holdings 1, LLC to WGR Operating, LP, Kerr-McGee Gathering LLC and Delaware Basin Midstream, LLC in exchange for aggregate consideration of $1.814 billion in cash, minus the outstanding amount payable pursuant to an intercompany note to be assumed in connection with the transaction, and 45,760,201 WES common units (the “Contribution”) and (ii) APC Midstream Holdings, LLC will sell to WES all of its interests in each of Saddlehorn Pipeline Company, LLC, a Delaware limited liability company, and Panola Pipeline Company, LLC, a Texas limited liability company, in exchange for aggregate consideration of $193.9 million in cash (the “Sale”). In addition, immediately prior to the Merger, all outstanding WES Class C units will be converted into WES common units on a one-for-one basis which, at the effective time of the Merger, will be converted into WGP common units at the exchange ratio. Further, WES and WES GP will cause the conversion of WES’s incentive distribution rights (“IDRs”) and the 2,583,068 general partner units held by WES GP into a non-economic general partner interest in WES and 105,624,704 WES common units, all of which will be held by WES GP. These WES common units, together

with 6,375,284 WES common units to be retained by WGRAH following the Contribution and 50,132,046 WES common units currently held by WGP, will remain outstanding following the Merger. For additional information regarding the Contribution, the Sale and the conversion of the WES Class C units, IDRs and general partner units, please see “Summary—Pre-Merger Transactions.”

WES is holding a special meeting of its unitholders at 1201 Lake Robbins Drive, The Woodlands, Texas 77380, on February 27, 2019 at 8:00 a.m., local time, to obtain the vote of its unitholders to approve the Merger Agreement and the transactions contemplated thereby, including the Merger. Your vote is very important regardless of the number of WES units you own. The Merger cannot be completed unless the holders of at least a majority of the outstanding WES common units and Class C units, each representing limited partner interests in WES, voting as a single class, vote for the approval of the Merger Agreement and the transactions contemplated thereby, including the Merger, at the special meeting. The WES GP Board recommends that WES unitholders vote “FOR” the approval of the Merger Agreement and the transactions contemplated thereby, including the Merger, and “FOR” the proposal to approve the adjournment of the special meeting, if necessary, to solicit additional proxies if there are not sufficient votes to approve the Merger Agreement and the transactions contemplated thereby, including the Merger, at the time of the special meeting. Pursuant to the Merger Agreement, WGP, which, as of November 7, 2018, directly or indirectly owned 50,132,046 WES common units, representing a 29.6% limited partner interest in WES, and APC, which, as of November 7, 2018, through subsidiaries other than WGP and WES GP, indirectly owned 2,011,380 WES common units and 14,045,429 Class C units, representing an aggregate 9.5% limited partner interest in WES, have each agreed to vote (or cause to be voted) all of the limited partner interests in WES then owned beneficially or of record by them or their respective subsidiaries in favor of the approval of the Merger Agreement, the transactions contemplated thereby, including the Merger, and any actions required in furtherance thereof. Whether or not you expect to attend the special meeting in person, we urge you to submit your proxy as promptly as possible through one of the delivery methods described in the accompanying proxy statement/prospectus.

In addition, we urge you to read carefully the accompanying proxy statement/prospectus (and the documents incorporated by reference therein), which includes important information about the Merger Agreement, the Merger and the special meeting. Please pay particular attention to the section titled “Risk Factors” beginning on page 20 of the accompanying proxy statement/prospectus.

On behalf of the WES GP Board, we thank you for your continued support.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities to be issued under the accompanying proxy statement/prospectus or determined that the accompanying proxy statement/prospectus is accurate or complete. Any representation to the contrary is a criminal offense.

The accompanying proxy statement/prospectus is dated January 28, 2019, and is first being mailed to the unitholders of WES on or about January 28, 2019.

Sincerely,

Benjamin M. Fink Chairman of the Board of Directors Western Gas Holdings, LLC (as general partner of Western Gas Partners, LP)

1201 Lake Robbins Drive

The Woodlands, Texas 77380

NOTICE OF SPECIAL MEETING OF UNITHOLDERS

TO BE HELD ON FEBRUARY 27, 2019

To the unitholders of Western Gas Partners, LP:

Notice is hereby given that a special meeting of unitholders of Western Gas Partners, LP (“WES”), will be held at 1201 Lake Robbins Drive, The Woodlands, Texas 77380, on February 27, 2019 at 8:00 a.m., local time, solely for the following purposes:

These items of business, including the Merger Agreement and the Merger, are described in detail in the accompanying proxy statement/prospectus. The board of directors of WES GP (the “WES GP Board”) has determined that the Merger Agreement and the transactions contemplated thereby, including the Merger, are advisable, fair and reasonable to and in the best interests of WES and its limited partners, and the special committee of the WES GP Board (the “WES Special Committee”) has unanimously, in good faith, determined that the Merger Agreement and the transactions contemplated thereby, including the Merger, are advisable, fair and reasonable to and in the best interests of WES and its limited partners (excluding WGP, APC and their respective affiliates) (the foregoing constituting “Special Approval” as defined in WES’s Second Amended and Restated Agreement of Limited Partnership, dated as of March 14, 2016, as heretofore amended (the “WES Partnership Agreement”)), and each of the WES GP Board and the WES Special Committee has unanimously, in good faith, approved the Merger Agreement and the transactions contemplated thereby, including the Merger. Therefore, the WES GP Board, based in part on the special approval and recommendation of the WES Special Committee, recommends that WES unitholders vote “FOR” the approval of the Merger Agreement and the transactions contemplated thereby, including the Merger, and “FOR” the proposal to approve the adjournment of the special meeting, if necessary, to solicit additional proxies in favor of such approval.

Only WES unitholders of record as of the close of business on January 14, 2019 are entitled to notice of the special meeting and to vote at the special meeting or at any adjournment thereof. A list of unitholders entitled to vote at the special meeting will be available in our offices, located at 1201 Lake Robbins Drive, The Woodlands, Texas 77380, during regular business hours for a period of 10 days before the special meeting, and at the place of the special meeting during the special meeting. Pursuant to the Merger Agreement, WGP and APC have each agreed to vote all of the limited partner interests in WES then owned beneficially or of record by them or their respective subsidiaries in favor of the approval of the Merger Agreement, the transactions contemplated thereby, including the Merger, and any actions required in furtherance thereof, which includes, if necessary, the

adjournment proposal. As of November 7, 2018, WGP directly or indirectly owned 50,132,046 WES common units, representing approximately 29.6% of the limited partner interests in WES entitled to vote at the special meeting, and APC, through subsidiaries other than WGP and WES GP, indirectly owned 2,011,380 WES common units and 14,045,429 Class C units, representing in the aggregate approximately 9.5% of the limited partner interests in WES entitled to vote at the special meeting.

Approval of the Merger Agreement and the transactions contemplated thereby, including the Merger, by the WES unitholders is a condition to the consummation of the Merger and requires the affirmative vote of the holders of at least a majority of the outstanding WES common units and Class C units voting as a single class. Therefore, your vote is very important. Your failure to vote your WES units will have the same effect as a vote “AGAINST” the approval of the Merger Agreement and the transactions contemplated thereby, including the Merger.

By order of the board of directors,

Philip H. Peacock Senior Vice President, General Counsel and Corporate Secretary Western Gas Holdings, LLC (as general partner of Western Gas Partners, LP)

The Woodlands, Texas

YOUR VOTE IS IMPORTANT!

WHETHER OR NOT YOU EXPECT TO ATTEND THE SPECIAL MEETING IN PERSON, WE URGE YOU TO SUBMIT YOUR PROXY AS PROMPTLY AS POSSIBLE (1) BY TELEPHONE, (2) VIA THE INTERNET OR (3) BY MARKING, SIGNING AND DATING THE ENCLOSED PROXY CARD AND RETURNING IT IN THE PREPAID ENVELOPE PROVIDED. You may revoke your proxy at any time before the special meeting. If your WES units are held in the name of a bank, broker or other fiduciary, please follow the instructions on the voting instruction card furnished to you by such record holder.

We urge you to read the accompanying proxy statement/prospectus, including all documents incorporated by reference therein, and its annexes carefully and in their entirety. If you have any questions concerning the Merger Agreement, the Merger, the adjournment vote, the special meeting or the accompanying proxy statement/prospectus or would like additional copies of the accompanying proxy statement/prospectus or need help voting your WES units, please contact WES’s proxy solicitor:

Morrow Sodali

509 Madison Avenue

Suite 1206

New York, NY 10022

Unitholders Call Toll Free: (800) 662-5200

Brokers call (203) 658-9400

E-mail: WES@morrowsodali.com

ADDITIONAL INFORMATION

This proxy statement/prospectus incorporates by reference important business and financial information about WGP and WES from other documents filed with the U.S. Securities and Exchange Commission (“SEC”) that are not included in or delivered with this proxy statement/prospectus.

Documents incorporated by reference are available to you without charge upon written or oral request. You can obtain any of these documents by visiting our website at http://www.westerngas.com or by writing or calling WGP or WES at the following addresses:

To receive timely delivery of the requested documents in advance of the special meeting, you should make your request no later than February 20, 2019.

For a more detailed description of the information incorporated by reference in this proxy statement/prospectus and how you may obtain it, see “Where You Can Find More Information.”

ABOUT THIS DOCUMENT

This document, which forms part of a registration statement on Form S-4 filed with the SEC by WGP (File No. 333-228864), constitutes a prospectus of WGP under Section 5 of the Securities Act of 1933, as amended (the “Securities Act”), with respect to the common units representing limited partner interests in WGP (“WGP common units”) to be issued pursuant to the Merger Agreement. This document also constitutes a notice of meeting and a proxy statement under Section 14(a) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), with respect to the special meeting of WES unitholders, at which WES unitholders will be asked to consider and vote on, among other matters, a proposal to approve the Merger Agreement and the transactions contemplated thereby, including the Merger.

You should rely only on the information contained in or incorporated by reference into this proxy statement/prospectus. No one has been authorized to provide you with information that is different from that contained in, or incorporated by reference into, this proxy statement/prospectus. This proxy statement/prospectus is dated January 28, 2019. The information contained in this proxy statement/prospectus is accurate only as of that date or, in the case of information in a document incorporated by reference, as of the date of such document, unless the information specifically indicates that another date applies. Neither the mailing of this proxy statement/prospectus to WES unitholders nor the issuance by WGP of WGP common units pursuant to the Merger Agreement will create any implication to the contrary.

This proxy statement/prospectus does not constitute an offer to sell, or a solicitation of an offer to buy, any securities, or the solicitation of a proxy, in any jurisdiction in which or from any person to whom it is unlawful to make any such offer or solicitation in such jurisdiction.

The information concerning WGP contained in this proxy statement/prospectus or incorporated by reference has been provided by WGP, and the information concerning WES contained in this proxy statement/prospectus or incorporated by reference has been provided by WES.

TABLE OF CONTENTS

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QUESTIONS AND ANSWERS

Set forth below are questions that you, as a unitholder of WES, may have regarding the merger proposal, the adjournment proposal and the special meeting, and brief answers to those questions. You are urged to read carefully this proxy statement/prospectus and the other documents referred to in this proxy statement/prospectus in their entirety, including the Merger Agreement, which is attached as Annex A to this proxy statement/prospectus, and the documents incorporated by reference into this proxy statement/prospectus, because this section may not provide all of the information that is important to you with respect to the Merger and the special meeting. You may obtain a list of the documents incorporated by reference into this proxy statement/prospectus in the section titled “Where You Can Find More Information.”

Q: Why am I receiving this proxy statement/prospectus?

A: WGP, WES and certain of their affiliates have agreed to, among other things, a Merger, pursuant to which Merger Sub, a wholly owned subsidiary of WGP, will merge with and into WES. WES will continue its existence as the surviving entity and a subsidiary of WGP, but WES common units will no longer be publicly traded. In order to complete the Merger, WES unitholders must vote to approve the Merger Agreement and the transactions contemplated thereby, including the Merger. WES is holding a special meeting of its unitholders to obtain such unitholder approval.

In connection with the Merger, WGP will issue WGP common units as the consideration to be paid to holders of WES common units. This document is being delivered to you as both a proxy statement of WES and a prospectus of WGP in connection with the Merger. It is the proxy statement by which the WES GP Board is soliciting proxies from you to vote on the approval of the Merger Agreement and the transactions contemplated thereby, including the Merger, at the WES special meeting or at any adjournment thereof. It is also the prospectus by which WGP will issue WGP common units to you in connection with the Merger.

Q: What will happen in the Merger?

A: Pursuant to the Merger Agreement, at the effective time of the Merger (the “effective time”), Merger Sub will merge with and into WES. WES will be the surviving limited partnership in the Merger and will be a subsidiary of WGP, but WES common units will no longer be publicly traded.

Pursuant to the Merger Agreement, immediately prior to the effective time, (i) AE&P and WGRAH (the “Contributing Parties”) will contribute all of their interests in each of Anadarko Wattenberg Oil Complex LLC, Anadarko DJ Oil Pipeline LLC, Anadarko DJ Gas Processing LLC, Wamsutter Pipeline LLC, DBM Oil Services, LLC, Anadarko Pecos Midstream LLC, Anadarko Mi Vida LLC and APC Water Holdings 1, LLC (“APCWH” and such interests, collectively, the “Contributed Interests”) to WGRO, KMGG and DBM (the “Recipient Parties”) in exchange for aggregate consideration of $1.814 billion in cash, minus the outstanding amount payable pursuant to an intercompany note (“the APCWH Note Payable”) to be assumed in connection with the transaction, and 45,760,201 WES common units (the “Contribution”) and (ii) AMH will sell to WES all of its interests in each of Saddlehorn Pipeline Company, LLC, a Delaware limited liability company, and Panola Pipeline Company, LLC, a Texas limited liability company (such interests, collectively, the “Purchased Interests”), in exchange for aggregate consideration of $193.9 million in cash (the “Sale”). In addition, immediately prior to the effective time, all outstanding WES Class C units will be converted into WES common units on a one-for-one basis which, at the effective time, will be converted into WGP common units at the exchange ratio (as defined below). Further, WES and WES GP will cause the conversion of WES’s incentive distribution rights (“IDRs”) and the 2,583,068 general partner units held by WES GP into a non-economic general partner interest in WES and 105,624,704 WES common units, all of which will be held by WES GP. These WES common units, together with 6,375,284 WES common units to be retained by WGRAH following the Contribution and 50,132,046 WES common units currently held by WGP, will remain outstanding following the Merger. We refer to the Merger together with the foregoing pre-Merger transactions as the “Transactions.” For additional information regarding the Contribution, the Sale and the conversion of the WES Class C units, IDRs and general partner units, please see “Summary—Pre-Merger Transactions.”

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Q: What will I receive in the Merger?

A: If the Merger is completed, each WES common unit issued and outstanding immediately prior to the effective time (other than WES common units owned by WGP or subsidiaries of WGP or WES GP and the WES common units to be issued in the Contribution) will be converted automatically into the right to receive 1.525 (the “exchange ratio”) WGP common units (the aggregate amount of such WGP common units, the “Merger Consideration”). WES common unitholders will not receive any fractional WGP common units in the Merger. Instead, all fractional WGP common units that a holder of WES common units would have been entitled to receive in the Merger will be aggregated and then, if a fractional WGP common unit results from that aggregation, be rounded up to the nearest whole WGP common unit. Based on the closing price of WGP common units on the New York Stock Exchange (the “NYSE”) on November 7, 2018, the last trading day prior to the public announcement of the Merger, the Merger Consideration was approximately $50.33 for each WES common unit. Based on the closing price of $30.46 for WGP common units on the NYSE on January 22, 2019, the most recent practicable trading day prior to the date of this proxy statement/prospectus, the Merger Consideration represents an equivalent value of approximately $46.45 for each WES common unit. The market price of WGP common units will fluctuate prior to the Merger, and the market price of WGP common units when received by WES common unitholders after the Merger is completed could be greater or less than the current market price of WGP common units. See “Risk Factors.”

Q: What will happen to the other series and classes of WES units in the Merger?

A: The Merger Agreement provides that immediately prior to the effective time, (i) the outstanding WES Class C units will be converted into WES common units on a one-for-one basis which, at the effective time, will be converted into WGP common units at the exchange ratio and (ii) all of the IDRs and the 2,583,068 general partner units in WES will be converted into a non-economic general partner interest in WES and 105,624,704 WES common units, all of which will be held by WES GP. These WES common units, together with 6,375,284 WES common units to be retained by WGRAH following the Contribution and 50,132,046 WES common units currently held by WGP, will remain outstanding following the Merger.

Q: What will the ownership of APC and its affiliates be in WGP following the completion of the Merger?

A: As of November 7, 2018, APC and its affiliates held 170,380,161 WGP common units, representing a 77.8% limited partner interest in WGP, and, through its ownership of WGP GP, APC indirectly held the non-economic general partner interest in WGP. Following the Contribution and the Merger, and based on the number of WES common units and WGP common units outstanding as of November 7, 2018 and Class C units expected to be outstanding immediately prior to the consummation of the Merger, APC and its affiliates will hold 251,320,496 WGP common units, representing a 55.5% limited partner interest in WGP, and through its ownership of WGP GP, APC will continue to indirectly hold the non-economic general partner interest in WGP. Please read “The Merger—Effect of the Merger” beginning on page 36 of this proxy statement/prospectus.

Q: What happens if the Merger is not completed?

A: If the Merger Agreement and the transactions contemplated thereby, including the Merger, are not approved by WES unitholders holding at least a majority of the outstanding WES common units and Class C units voting as a single class, or if the Merger is not completed for any other reason, you will not receive any form of consideration for your WES common units in connection with the Merger. Instead, WES will remain an independent publicly traded limited partnership and the WES common units will continue to be listed and traded on the NYSE.

The Merger Agreement contains certain termination rights for each of WES, WGP or APC, including in the event that (a) the Merger and the other transactions contemplated by the Merger Agreement have not been

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consummated by June 30, 2019, (b) there is any final and nonappealable law, injunction, judgment, ruling or agreement enacted, promulgated, issued, entered, amended, enforced by or entered into with any governmental authority enjoining, restraining, preventing or prohibiting the consummation of the Merger and the other transactions contemplated by the Merger Agreement or (c) the requisite WES unitholder approval is not obtained. In addition, WGP may terminate the Merger Agreement in the event that, prior to the time WES unitholder approval is obtained, the WES Special Committee or the WES GP Board shall have changed its recommendation to WES unitholders with respect to the merger proposal (a “WES change in recommendation”). Upon termination of the Merger Agreement by WGP due to a WES change in recommendation, WES shall be required to pay WGP a termination fee of $60.0 million in cash. Please read “Proposal 1: The Merger Agreement—Change in WES Special Committee Recommendation or WES GP Board Recommendation” beginning on page 77 of this proxy statement/prospectus.

Q: Will I continue to receive future distributions on my WES common units?

A: Before completion of the Merger, WES expects to continue to pay its regular quarterly cash distribution on the WES common units, which was $0.965 per WES common unit for the quarter ended September 30, 2018. However, WGP and WES will coordinate the timing of distribution declarations leading up to completion of the Merger so that, in any quarter, a holder of WES common units will either receive distributions in respect of its WES common units or distributions in respect of the WGP common units that such holder will receive as Merger Consideration (but will not receive distributions from both WES and WGP in any single quarter). Receipt of the regular quarterly distribution will not reduce the Merger Consideration you receive. Upon completion of the Merger, you will be entitled only to distributions on any WGP common units you hold through the applicable distribution record date. While WGP provides no assurances as to the level or payment of any future distributions on the WGP common units, and WGP reserves to itself the sole right to determine the amount of its distributions each quarter, with respect to the quarter ended September 30, 2018, WGP paid a cash distribution of $0.595 per WGP common unit on November 21, 2018 to holders of record as of the close of business on October 31, 2018. For additional information, please read “Comparative Unit Prices and Distributions.”

Q: What am I being asked to vote on?

A: WES’s unitholders are being asked to vote on the following proposals:

The approval of the merger proposal by WES unitholders holding at least a majority of the outstanding WES common units and Class C units voting as a single class is a condition to the obligations of WGP and WES to complete the Merger. The adjournment proposal is not a condition to the obligations of WGP or WES to complete the Merger.

Q: Does the WES GP Board recommend that WES common unitholders approve the Merger Agreement and the transactions contemplated thereby?

A: Yes. The WES GP Board has unanimously, in good faith, determined that the Merger Agreement and the transactions contemplated thereby, including the Merger, are advisable, fair and reasonable to and in the best interests of WES and its limited partners, following the recommendation of the WES Special Committee that the Merger Agreement and the transactions contemplated thereby, including the Merger are advisable, fair and reasonable to and in the best interests of WES and its limited partners (excluding WGP, APC and their respective affiliates) (the foregoing constituting “Special Approval” as defined in the WES Partnership Agreement), and

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each of the WES GP Board and the WES Special Committee has unanimously, in good faith, approved the Merger Agreement and the transactions contemplated thereby, including the Merger. Therefore, the WES GP Board, based in part on the recommendation and special approval of the WES Special Committee, recommends that you vote “FOR” the approval of the Merger Agreement and the transactions contemplated thereby, including the Merger, and “FOR” the proposal to approve the adjournment of the special meeting, if necessary, to solicit additional proxies if there are not sufficient votes to approve the Merger Agreement and the transactions contemplated thereby, including the Merger, at the time of the special meeting. See “The Merger—Recommendation of the WES GP Board; Reasons for the Merger” beginning on page 47 of this proxy statement/prospectus. In considering the recommendation of the WES GP Board with respect to the Merger Agreement and the transactions contemplated thereby, including the Merger, you should be aware that directors and executive officers of WES GP are parties to agreements or participants in other arrangements that give them interests in the Merger that may be different from, or in addition to, your interests as a unitholder of WES. You should consider these interests in voting on the merger proposal. These different interests are described under “The Merger—Interests of Directors and Executive Officers of WES GP in the Merger” beginning on page 68 of this proxy statement/prospectus.

Q: What unitholder vote is required for the approval of each proposal?

A: The following are the vote requirements for the WES proposals:

Pursuant to the Merger Agreement, WGP and APC have each agreed to vote all of the limited partner interests in WES then owned beneficially or of record by them or their respective subsidiaries in favor of the approval of the Merger Agreement, the transactions contemplated thereby, including the Merger, and any actions required in furtherance thereof, which includes, if necessary, the adjournment proposal. As of November 7, 2018, WGP directly or indirectly owned 50,132,046 WES common units, representing approximately 29.6% of the limited partner interests in WES entitled to vote at the special meeting, and APC, through subsidiaries other than WGP and WES GP, indirectly owned 2,011,380 WES common units and 14,045,429 Class C units, representing in the aggregate approximately 9.5% of the limited partner interests in WES entitled to vote at the special meeting.

Q: What constitutes a quorum for the special meeting?

A: The holders of at least a majority of the outstanding WES common units and Class C units taken as a single class must be represented in person or by proxy at the special meeting in order to constitute a quorum.

Q: When is this proxy statement/prospectus being mailed?

A: This proxy statement/prospectus and the proxy card are first being sent to WES unitholders on or about January 28, 2019.

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Q: Who is entitled to vote at the special meeting?

A: Holders of WES common units and Class C units outstanding as of the close of business on January 14, 2019 (the “record date”) are entitled to one vote per unit at the special meeting.

As of the record date, there were approximately 152,609,285 WES common units and 14,372,665 WES Class C units outstanding, all of which are entitled to vote at the special meeting.

Q: When and where is the special meeting?

A: The special meeting will be held at 1201 Lake Robbins Drive, The Woodlands, Texas 77380, on February 27, 2019, at 8:00 a.m., local time.

Q: How do I vote my WES units at the special meeting?

A:    There are four ways you may cast your vote. You may vote:

Even if you plan to attend the special meeting in person, you are encouraged to submit your proxy as described above so that your vote will be counted if you later decide not to attend the special meeting.

If your WES units are held by a bank, broker or other nominee, also known as holding units in “street name,” you should receive instructions from the bank, broker or other nominee that you must follow in order to have your WES units voted. Please review such instructions to determine whether you will be able to submit your proxy via Internet or by telephone. The deadline for submitting your proxy by telephone or electronically through the Internet is 11:59 p.m., Eastern Time, on February 26, 2019 (the “telephone/internet deadline”). However, if the special meeting is adjourned to solicit additional proxies, the deadline may be extended.

Q: If my WES units are held in “street name” by my broker, will my broker automatically vote my WES units for me?

A: No. If your WES units are held in an account at a broker or through another nominee, you must instruct the broker or other nominee on how to vote your WES units by following the instructions that the broker or other nominee provides to you with these materials. Most brokers offer the ability for unitholders to submit voting instructions by mail by completing a voting instruction card, by telephone and via the Internet.

If you do not provide voting instructions to your broker, your WES units will not be voted on any proposal on which your broker does not have discretionary authority to vote. This is referred to in this proxy

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statement/prospectus and in general as a broker non-vote. In these cases, the broker can register your WES units as being present at the special meeting for purposes of determining a quorum, but will not be able to vote on those matters for which specific authorization is required. Under the current rules of the NYSE, brokers do not have discretionary authority to vote on either of the proposals at the special meeting, including the merger proposal. A broker non-vote will have the same effect as a vote “AGAINST” the merger proposal and the adjournment proposal.

Q: How will my WES units be represented at the special meeting?

A: If you properly submit your proxy by telephone, via the Internet website or by signing and returning your proxy card, the officers named in your proxy card will vote your WES units in the manner you requested. If you sign your proxy card and return it without indicating how you would like to vote your WES units, your proxy will be voted as the WES GP Board recommends, which is:

Q: Who may attend the special meeting?

A: WES common and Class C unitholders (or their authorized representatives) and WES’s invited guests may attend the special meeting. All attendees at the special meeting should be prepared to present government-issued photo identification (such as a driver’s license or passport) for admittance.

Q: Is my vote important?

A: Yes, your vote is very important. If you do not submit a proxy or vote in person at the special meeting, it will be more difficult for WES to obtain the necessary quorum to hold the special meeting. In addition, an abstention or your failure to submit a proxy or to vote in person will have the same effect as a vote “AGAINST” the approval of the Merger Agreement and the transactions contemplated thereby, including the Merger. If you hold your WES units through a bank, broker or other nominee, your bank, broker or other nominee will not be able to cast a vote on such approval without instructions from you. The WES GP Board, based in part on the recommendation and special approval of the WES Special Committee, recommends that WES unitholders vote “FOR” the merger proposal.

Q: Can I revoke my proxy or change my voting instructions?

A: Yes. If you are a WES unitholder of record, you may revoke or change your proxy at any time before the telephone/internet deadline or before the polls close at the special meeting by:

If you hold your WES units through a bank, broker or other nominee, you must follow the directions you receive from your bank, broker or other nominee in order to revoke your proxy or change your voting instructions.

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Q: What happens if I sell my WES common units after the record date but before the special meeting?

A: The record date for the special meeting is earlier than the date of the special meeting and earlier than the date that the Merger is expected to be completed. If you sell or otherwise transfer your WES units after the record date but before the date of the special meeting, you will retain your right to vote at the special meeting. However, you will not have the right to receive the Merger Consideration to be received by WES’s common unitholders in the Merger. In order to receive the Merger Consideration, you must hold the WES common units entitled thereto through the effective time.

Q: What does it mean if I receive more than one proxy card or vote instruction card?

A: Your receipt of more than one proxy card or vote instruction card may mean that you have multiple accounts with WES’s transfer agent or with a bank, brokerage firm or other nominee. If voting by mail, please sign and return all proxy cards or vote instruction cards to ensure that all of your WES units are voted. Each proxy card or vote instruction card represents a distinct number of units and it is the only means by which those particular units may be voted by proxy.

Q: Is completion of the Merger subject to any conditions?

A: Yes. In addition to the approval of the Merger Agreement by the holders of at least a majority of the outstanding WES common units and Class C units voting as a single class, completion of the Merger is subject to the satisfaction or waiver of customary closing conditions, including, among others: (1) the completion of certain transactions other than the Merger pursuant to the Merger Agreement, including the Contribution and the Sale, on the date of the closing of the Merger, (2) there having been obtained any required approval or consent under applicable antitrust law, (3) there being no law or injunction prohibiting the consummation of the Merger or pre-Merger transactions, (4) the effectiveness of the Registration Statement on Form S-4 of which this proxy statement/prospectus forms a part and (5) approval for listing of the Merger Consideration on the NYSE.

Q: When do you expect to complete the Merger?

A: WGP and WES are working towards completing the Merger promptly. WGP and WES currently expect to complete the Merger shortly following the conclusion of the special meeting, subject to receipt of the WES unitholder approval, the closing of the Contribution and the Sale, regulatory approvals and clearances and other usual and customary closing conditions; however, no assurance can be given as to when, or if, the Merger will occur.

Q: What are the expected U.S. federal income tax consequences to a WES unitholder as a result of the transactions contemplated by the Merger Agreement?

A: No gain or loss should be recognized by a holder of WES units solely as a result of the receipt of the Merger Consideration, other than (A) gain resulting from a decrease in the WES common unitholder’s share of liabilities pursuant to Section 752 of the Code, (B) gain resulting from the application of Treasury Regulation Section 1.707-3(a)(1) to amounts treated as a transfer of consideration, (C) gain resulting from the application of Section 897 of the Code to a WES unitholder that is not a U.S. person, and (D) gain resulting from a deemed sale of WGP common units pursuant to Section 2.2(j) of the Merger Agreement. The amount and effect of any gain that may be recognized by holders of WES units will depend on such unitholder’s particular situation, including the ability of such unitholder to utilize any suspended passive losses.

Further, while we generally do not expect the WES unitholders to be subject to withholding obligations as a result of the transactions contemplated by the Merger Agreement, a WES unitholder whose WGP common units are deemed to be sold to fulfill its withholding obligations should recognize gain equal to the excess of the fair market value of the WGP common units which are deemed to be sold over the WES unitholder’s adjusted tax basis in such WGP common units.

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For additional information, please read “Material U.S. Federal Income Tax Consequences of the Merger—Tax Consequences of the Merger to WES and WES Common Unitholders” and “Risk Factors—Risks Related to the Merger.”

Q: What are the expected U.S. federal income tax consequences for a WES unitholder of the ownership of WGP common units after the Merger is completed?

A: Each WES unitholder who becomes a holder of WGP common units as a result of the Merger will, as is the case for existing WGP common unitholders, be allocated such unitholder’s distributive share of WGP’s income, gains, losses, deductions and credits. In addition to U.S. federal income taxes, such a holder will be subject to other taxes, including state and local income taxes, unincorporated business taxes, and estate, inheritance or intangibles taxes that may be imposed by the various jurisdictions in which WGP conducts business or owns property following the Merger, or in which the unitholder is a resident. Please read “Material U.S. Federal Income Tax Consequences of Owning WGP Common Units.”

Q: How many Schedules K-1 will I receive for 2019 if I am a WES unitholder?

A: If you are a holder of WES units, you will receive two Schedules K-1, one from WES, which will describe your share of WES’s income, gain, loss and deduction for the portion of the tax year that you held WES units prior to the effective time, and one from WGP, which will describe your share of WGP’s income, gain, loss and deduction for the portion of the tax year you held WGP common units following the effective time.

WES expects to furnish a Schedule K-1 to each existing WES unitholder within 90 days of the closing of WES’s taxable year on December 31, 2019, and WGP expects to furnish a Schedule K-1 to each WGP common unitholder within 90 days of the closing of WGP’s taxable year on December 31, 2019.

Q: What do I need to do now?

A: Carefully read and consider the information contained in and incorporated by reference into this proxy statement/prospectus, including its annexes. Then, please submit your proxy or vote your WES units in accordance with the instructions described above.

If you hold WES common units through a bank, broker or other nominee, please instruct your bank, broker or nominee to vote your common units by following the instructions that the bank, broker or nominee provides to you with these materials.

Q: Should I send in my unit certificates now?

A: No. WES unitholders should not send in their unit certificates at this time. After completion of the Merger, WGP’s exchange agent will send you a letter of transmittal and instructions for exchanging your WES units for the Merger Consideration.

Q: Are holders of WES units entitled to dissenters’ rights or appraisal rights?

A: No. Neither dissenters’ rights nor appraisal rights are available in connection with the Merger under the Delaware Revised Uniform Limited Partnership Act (the “Delaware LP Act”), the Merger Agreement or the WES Partnership Agreement.

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Q: Whom should I call with questions?

A: WES unitholders who have questions about the Merger Agreement, the Merger or the special meeting, or who desire additional copies of this proxy statement/prospectus or additional proxy cards or voting instruction forms, should contact Morrow Sodali LLC, WES’s proxy solicitor, at:

Morrow Sodali

509 Madison Avenue

Suite 1206

New York, NY 10022

Unitholders Call Toll Free: (800) 662-5200

Brokers call (203) 658-9400

E-mail: WES@morrowsodali.com

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RISK FACTORS

In addition to the other information included and incorporated by reference into this proxy statement/prospectus, including the matters addressed in the section titled “Cautionary Statement Regarding Forward-Looking Statements,” you should carefully consider the following risks before deciding whether to vote for the approval of the Merger Agreement and the transactions contemplated thereby, including the Merger. You should also read and carefully consider the risks associated with each of WGP and WES and their respective businesses. These risks can be found in WGP’s and WES’s respective Annual Reports on Form 10-K for the year ended December 31, 2017, as updated by any subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, which are filed with the SEC and incorporated by reference into this proxy statement/prospectus. For further information regarding the documents incorporated into this proxy statement/prospectus by reference, please see the section titled “Where You Can Find More Information.” Realization of any of the risks described below, any of the events described under “Cautionary Statement Regarding Forward-Looking Statements” or any of the risks or events described in the documents incorporated by reference herein could have a material adverse effect on WGP’s or WES’s business, financial condition, cash flows and results of operations and could result in a decline in the trading prices of their respective common units.

Risks Related to the Merger

Because the market price of WGP common units will fluctuate prior to the consummation of the Merger, WES common unitholders cannot be sure of the market value of the WGP common units they will receive as Merger Consideration relative to the value of WES common units they exchange.

The market value of the Merger Consideration that WES common unitholders will receive in the Merger will depend on the trading price of WGP’s common units at the closing of the Merger. The exchange ratio that determines the number of WGP common units that WES common unitholders will receive as Merger Consideration is fixed. This means that there is no mechanism contained in the Merger Agreement that will adjust the number of WGP common units that WES common unitholders will receive as Merger Consideration to account for any decreases or increases in the trading price of WGP common units. Unit price changes may result from a variety of factors (many of which are beyond WGP’s or WES’s control), including:

Because the Merger will be completed after the special meeting, at the time of the meeting, you will not know the exact market value of the WGP common units that you will receive upon completion of the Merger. If WGP’s common unit price at the closing of the Merger is less than WGP’s common unit price on the date on which the Merger Agreement was signed, then the market value of the Merger Consideration received by WES common unitholders will be less than contemplated at the time the Merger Agreement was signed.

The fairness opinion rendered to the WES Special Committee by Lazard was based on Lazard’s financial analysis and considered factors such as market and other conditions then in effect, financial forecasts and other information made available to Lazard as of the date of the opinion. As a result, the opinion does not reflect changes in events or circumstances after the date of such opinion. The WES Special Committee has not obtained, and does not expect to obtain, an updated fairness opinion from Lazard reflecting changes in circumstances that may have occurred since the signing of the Merger Agreement.

The fairness opinion rendered to the WES Special Committee by Lazard was provided in connection with, and at the time of, the evaluation of the Merger and the Merger Agreement by the WES Special Committee. The

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opinion was based on the financial analyses performed, which considered market and other conditions then in effect, the Unaudited Financial Projections (dated October 24, 2018) and other information made available to Lazard as of the date of the opinion, which may have changed, or may change, after the date such information was prepared or after the date of the opinion. The WES Special Committee has not obtained an updated opinion from Lazard following the date of the Merger Agreement and does not expect to obtain an updated opinion prior to completion of the Merger. Changes in the operations and prospects of WGP or WES, general market and economic conditions and other factors that may be beyond the control of WGP and WES, and on which the fairness opinion was based, may have altered the value of WGP or WES or the prices of WGP common units or WES common units since the date of such opinion, or may alter such values and prices by the time the Merger is completed. The opinion does not speak as of any date other than the date of the opinion. For a description of the opinion that Lazard rendered to the WES Special Committee, a copy of which is attached to this proxy statement/prospectus as Annex B, please refer to “The Merger—Opinion of the Financial Advisor to the WES Special Committee.”

WES and WGP may be targets of securities class action and derivative lawsuits, which could result in substantial costs and may delay or prevent the completion of the Merger.

Securities class action lawsuits and derivative lawsuits are often brought against companies that have entered into merger agreements in an effort to enjoin the subject transactions or seek monetary relief from the parties thereto. Even if the lawsuits are without merit, defending against these claims can result in substantial costs and divert management time and resources. WES and WGP cannot predict the likelihood or outcome of any such lawsuits, or others, nor can they predict the amount of time and expense that would be required to resolve such litigation. An unfavorable resolution of any litigation related to the Merger could delay or prevent its consummation. In addition, the costs of defending the litigation, even if resolved in WES’s or WGP’s favor, could be substantial and such litigation could distract WES and WGP from pursuing the consummation of the Merger and other potentially beneficial business opportunities.

WES’s and WGP’s financial estimates are based on various assumptions that may not prove to be correct.

The financial estimates set forth in the forecast included under “The Merger—Unaudited Financial Projections” are based on assumptions of, and information available to, WES and WGP, as of October 24, 2018, the time they were prepared. Neither WES nor WGP knows whether such assumptions will prove correct. Any or all of such estimates may not necessarily be realized. Such estimates can be adversely affected by inaccurate assumptions or by known or unknown risks and uncertainties, many of which are beyond WES’s and WGP’s control. Many factors mentioned in this proxy statement/prospectus, including the risks outlined in this “Risk Factors” section and the events or circumstances described under “Cautionary Statement Regarding Forward-Looking Statements,” will be important in determining WES’s and WGP’s future results. As a result of these contingencies, actual future results may vary materially from WES’s and WGP’s estimates. In view of these uncertainties, the inclusion of WES’s and WGP’s financial estimates in this proxy statement/prospectus is not and should not be viewed as a representation that the forecast results will be achieved.

The Unaudited Financial Projections were not prepared with a view toward public disclosure, and such financial estimates were not prepared with a view toward compliance with published guidelines of any regulatory or professional body. Further, any forward-looking statement speaks only as of the date on which it is made, and WES and WGP undertake no obligation, other than as required by applicable law, to update their respective financial estimates herein to reflect events or circumstances after the date those financial estimates were prepared or to reflect the occurrence of anticipated or unanticipated events or circumstances.

The Unaudited Financial Projections included in this proxy statement/prospectus have been prepared by, and are the responsibility of, WES and WGP individually. Moreover, neither WES’s or WGP’s independent accountants, KPMG LLP, nor any other independent accountants, have compiled, examined or performed any procedures with respect to the Unaudited Financial Projections contained herein, nor have they expressed any

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opinion or any other form of assurance on such information or its achievability, and, accordingly, KPMG LLP assumes no responsibility for, and disclaims any association with, the Unaudited Financial Projections. The reports of KPMG LLP incorporated by reference herein relate exclusively to the historical audited financial information of the entities named in those reports and do not cover any other information in this proxy statement/prospectus and should not be read to do so. See “The Merger—Unaudited Financial Projections” for more information.

Directors and executive officers of WES GP have certain interests that are different from those of WES unitholders generally.

Directors and executive officers of WES GP are parties to agreements or participants in other arrangements that give them interests in the Merger that may be different from, or in addition to, your interests as a unitholder of WES. In addition, certain of the directors and executive officers of WES GP are also directors or officers of WGP GP and/or APC. Each of the directors of WES GP is appointed by WGP, as the sole member of WES GP, and each of the directors of WGP GP is appointed by APC through its control of WGP GP. These and other different interests are described under “The Merger—Interests of Directors and Executive Officers of WES GP in the Merger.” You should consider these interests in voting on the merger proposal.

The WES Partnership Agreement limits the duties of WES GP to WES unitholders and restricts the remedies available to unitholders for actions taken by WES GP that might otherwise constitute breaches of its duties.

WES GP, which is the general partner of WES, is owned by WGP. In light of potential conflicts of interest between WGP and WES GP, on the one hand, and WES and WES unitholders, on the other hand, the WES GP Board submitted the Merger and related matters to the WES Special Committee for, among other things, review, evaluation, negotiation and possible approval of a majority of its members, which is referred to as “Special Approval” in the WES Partnership Agreement and this proxy statement/prospectus. The duties of WES GP, the WES GP Board and the WES Special Committee to WES unitholders in connection with the Merger are substantially limited by the WES Partnership Agreement. Specifically, under the WES Partnership Agreement:

The WES Special Committee reviewed, negotiated and evaluated the Merger Agreement, the Merger and related matters on behalf of WES and WES’s limited partners (excluding WGP, APC and their respective affiliates). Among other things, the WES Special Committee unanimously determined in good faith that the Merger Agreement and the transactions contemplated thereby, including the Merger, are advisable, fair and reasonable to and in the best interests of WES and its limited partners (excluding WGP, APC and their respective affiliates), approved the Merger Agreement and the transactions contemplated thereby, including the Merger, and recommended the approval of the Merger Agreement and the transactions contemplated thereby, including the Merger, to the WES GP Board.

WGP common unitholders have limited voting rights and are not entitled to elect WGP’s general partner or the directors of WGP’s general partner.

Unlike the holders of common stock in a corporation, WGP common unitholders have only limited voting rights on matters affecting WGP’s business, and therefore limited ability to influence WGP management’s

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decisions regarding its business. WGP common unitholders did not elect its general partner and will have no right to elect its general partner or the officers or directors of its general partner on an annual or other continuing basis. In addition, on matters where WGP common unitholders are entitled to vote, the WGP Partnership Agreement generally permits WGP GP and its affiliates to vote their WGP common units on such matters, together with unaffiliated WGP unitholders, as a single class. For example, WGP GP may only be removed as the general partner by the affirmative vote of holders of 80% of the WGP common units (including WGP GP and its affiliates), voting together as a single class. As of November 7, 2018, WGP GP and its affiliates, including APC, collectively own approximately 77.8% of the outstanding WGP common units. Following the closing of the Contribution, the Sale, the Merger and the issuance of the Merger Consideration to former WES common unitholders, the percentage ownership of WGP GP and its affiliates, including APC, of WGP common units is expected to be approximately 55.5%.

WGP common units to be received by WES common unitholders as a result of the Merger have different rights than WES common units.

Following completion of the Merger, WES common unitholders will no longer hold WES common units, but will instead be common unitholders of WGP. There are differences between the rights of WES common unitholders and the rights of WGP common unitholders. See “Comparison of Rights of WGP Common Unitholders and WES Common Unitholders” for a discussion of the different rights associated with WGP common units and WES common units.

The number of outstanding WGP common units will increase as a result of the Merger, which could make it more difficult for WGP to pay the current level of quarterly distributions.

As of November 7, 2018, there were 218,937,797 WGP common units outstanding. WGP expects to issue approximately 234,150,770 common units in connection with the Merger. Accordingly, the aggregate dollar amount required to pay the current per unit quarterly distribution on all WGP common units will increase, which could increase the likelihood that WGP will not have sufficient funds to pay the current level of quarterly distributions to all WGP unitholders. Using a $0.595 per WGP common unit distribution (the amount WGP paid with respect to the third fiscal quarter of 2018 on November 21, 2018, to holders of record as of October 31, 2018), the aggregate cash distribution paid to WGP unitholders totaled approximately $130 million. Using the same $0.595 per WGP common unit distribution, the combined pro forma WGP distribution with respect to the third fiscal quarter of 2018, had the transactions contemplated by the Merger Agreement, including the Merger and the issuance of the Merger Consideration, been completed prior to such distribution, would have resulted in total cash distributions of approximately $269.6 million.

WGP and WES will incur substantial transaction-related costs in connection with the Merger, including fees paid to legal, financial and accounting advisors, filing fees and printing costs.

WGP and WES expect to incur a number of non-recurring transaction-related costs associated with completing the Merger. These fees and costs will be substantial. Non-recurring transaction costs include, but are not limited to, fees paid to legal, financial and accounting advisors, filing fees and printing costs. Thus, any net benefit of the Merger may not be achieved in the near term, the long term or at all.

The Merger is subject to conditions, including certain conditions that may not be satisfied on a timely basis, if at all. Failure to complete the Merger, or significant delays in completing the Merger, could negatively affect the trading prices of WGP common units and WES common units and the future business and financial results of WGP and WES.

The completion of the Merger is subject to a number of conditions, some of which are beyond the parties’ control. The completion of the Merger is not assured and is subject to risks, including the risk that the closing conditions are not satisfied, the approval of the Merger by WES unitholders or by governmental agencies is not

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obtained or the occurrence of a material adverse change to the business or results of operations of WGP and WES. The failure to satisfy the conditions to the Merger may prevent or delay the Merger or otherwise result in the Merger not occurring. The failure to complete the Merger, or any significant delays in completing the Merger, could cause WGP not to realize, or delay the realization of, some or all of the benefits that it expects to achieve from the Merger. In addition, the future trading price of WGP common units and the respective future business and financial results of WGP and WES are subject to risks, including the following:

In addition, the Merger Agreement contains certain termination rights for each of WES, WGP or APC, including in the event that (a) the Merger and the pre-Merger transactions have not been consummated by June 30, 2019, (b) there is any final and nonappealable law, injunction, judgment, ruling or agreement enacted, promulgated, issued, entered, amended, enforced by or entered into with any governmental authority enjoining, restraining, preventing or prohibiting the consummation of the Merger and the pre-Merger transactions or (c) the requisite WES unitholder approval is not obtained. In addition, WGP may terminate the Merger Agreement in the event that, prior to the time WES unitholder approval is obtained, the WES Special Committee or the WES GP Board shall have made a WES change in recommendation. Upon termination of the Merger Agreement by WGP due to a WES change in recommendation, WES shall be required to pay WGP a termination fee equal to $60.0 million in cash. Please read “Proposal 1: The Merger Agreement—Change in WES Special Committee Recommendation or WES GP Board Recommendation” beginning on page 77 of this proxy statement/prospectus.

In specified circumstances under the Merger Agreement, WES would be required to pay a termination fee to WGP of $60.0 million in cash.

Under the Merger Agreement, WES is required to conduct its business in the ordinary course of business consistent with past practice. Specifically, WES has agreed not to merge into or with any other company or adopt a plan of complete or partial liquidation or resolutions providing for or authorizing its liquidation, dissolution, recapitalization, restructuring, or other reorganization. In addition, under the Merger Agreement, in the event of a WES change in recommendation with respect to the proposed Merger, WES must provide WGP with five calendar days’ notice to allow WGP to propose an adjustment to the terms and conditions of the Merger Agreement. These provisions could discourage a third party that may have an interest in acquiring all or a significant part of WES from considering or proposing that acquisition, even if such third party were prepared to pay consideration with a higher per unit market value than the Merger Consideration, or might result in a potential competing acquirer of WES proposing to pay a lower price than it would otherwise have proposed to pay because of the added expense of the $60.0 million cash termination fee that would become payable in the event of a termination of the Merger Agreement by WGP due to a WES change in recommendation.

If a governmental authority asserts objections to the Merger, WGP and WES may be unable to complete the Merger or, in order to do so, WGP and WES may be required to comply with material restrictions or satisfy material conditions.

The closing of the Merger is subject to the condition that there is no final and nonappealable law, injunction, judgment, ruling or agreement enacted, promulgated, issued, entered, amended, enforced by or entered into with any governmental authority enjoining, restraining, preventing or prohibiting the consummation of the Merger and

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the pre-Merger transactions. If a U.S. governmental authority asserts objections to the Merger, WGP or WES may be required to divest assets, rescind the agreements or accept other remedies in order to complete the Merger. There can be no assurance as to the cost, scope or impact of the actions that may be required to address any governmental authority’s objections to the Merger. If WGP or WES takes such actions, it could be detrimental to it or to WGP’s ongoing business following the consummation of the Merger. Furthermore, these actions could have the effect of delaying or preventing completion of the proposed Merger or imposing additional costs on or limiting the revenues or cash available for distribution by WGP following the consummation of the Merger. See “The Merger—Antitrust and Regulatory Matters.”

Additionally, state attorneys general or other state or local regulators could seek to block, rescind or challenge the Merger as they deem necessary or desirable in the public interest at any time, including after the effective time. In addition, in some circumstances, a third party could initiate a private action under antitrust laws challenging or seeking to enjoin or rescind the Merger, before or after it is completed. WGP may not prevail and may incur significant costs in defending or settling any action under the antitrust laws.

WGP and WES are subject to contractual interim operating restrictions while the proposed Merger is pending, which could adversely affect each party’s business and operations.

Under the terms of the Merger Agreement, each of WGP and WES is subject to certain restrictions on the conduct of its business prior to completing the Merger, which may adversely affect their ability to execute certain of their business strategies. Such limitations could negatively affect each party’s businesses and operations prior to the completion of the Merger. For a discussion of these restrictions, see “Proposal 1: The Merger Agreement—Conduct of Business Pending the Consummation of the Merger.”

If the Merger is approved by WES unitholders, the date on which WES common unitholders will receive the Merger Consideration is uncertain.

As described in this proxy statement/prospectus, the completion of the proposed Merger is subject to several conditions, not all of which are controllable or waivable by WGP or WES. Accordingly, if the proposed Merger is approved by WES common unitholders, the date on which WES common unitholders will receive the Merger Consideration depends on the completion date of the Merger, which is uncertain.

WES unitholders will have a reduced ownership in WGP after the Merger as compared to their ownership of WES prior to the Merger.

At the effective time of the Merger, each WES unitholder that receives WGP common units will become a common unitholder of WGP, with a percentage ownership of WGP that is smaller than such unitholder’s percentage ownership of WES prior to the Merger. Assuming that the Merger had been completed on November 7, 2018, current WES common unitholders (other than APC, WGP and their respective affiliates) would have owned approximately 33.8% of WGP based on the number of WES common units and WGP common units outstanding on that date and Class C units expected to be outstanding immediately prior to the consummation of the Merger.

No ruling has been obtained with respect to the U.S. federal income tax consequences of the Merger.

No ruling has been obtained or will be requested from the IRS with respect to the U.S. federal income tax consequences of the Merger. Instead, WGP and WES are relying on the opinions of their counsel as to the U.S. federal income tax consequences of the Merger, and such counsel’s conclusions may not be sustained if challenged by the IRS. Please read “Material U.S. Federal Income Tax Consequences of the Merger.”

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The expected U.S. federal income tax consequences of the Merger are dependent upon WGP and WES being treated as partnerships for U.S. federal income tax purposes.

If either WGP or WES were to be treated as a corporation for U.S. federal income tax purposes, the consequences of the Merger would be materially different. If WGP were to be treated as a corporation for U.S. federal income tax purposes, the Merger would likely be a fully taxable transaction to WES common unitholders.

WES common unitholders could recognize taxable income or gain for U.S. federal income tax purposes as a result of the Merger.

For U.S. federal income tax purposes, each holder of WES common units (other than WGP, its subsidiaries, and, with respect to WGRAH’s retained WES common units, WGRAH) will be deemed to contribute its WES common units to WGP in exchange for WGP common units and the deemed assumption by WGP of each such WES common unitholder’s share of WES’s liabilities. The deemed assumption by WGP of such liabilities will trigger gain or loss to such WES common unitholders to the extent that such amounts are treated as a “disguised sale” of property, rather than as a non-taxable contribution of WES common units to WGP in exchange for WGP common units. In addition, as a result of the Merger, the holders of WES common units who receive WGP common units will become limited partners of WGP and will be allocated a share of WGP’s nonrecourse liabilities. Each holder of WES common units will be treated as receiving a deemed cash distribution equal to the net reduction in the amount of nonrecourse liabilities allocated to such WES common unitholder (as adjusted to take into account any nonrecourse liabilities included in the Section 707 Consideration (as defined below)). If the amount of such deemed cash distribution received by a holder of WES common units exceeds such WES common unitholder’s tax basis in WGP common units immediately after the Merger, after reducing such tax basis to account for any tax basis allocable to the portion of such unitholder’s WES common units deemed sold as a result of the receipt of Section 707 Consideration, such WES common unitholder will recognize gain in an amount equal to such excess. Further, while under current law we generally do not expect the WES common unitholders to be subject to withholding obligations as a result of the transactions contemplated by the Merger Agreement, a WES common unitholder whose WGP common units are deemed to be sold to fulfil its withholding obligations should recognize gain equal to the excess of the fair market value of the WGP common units which are deemed to be sold over the WES common unitholder’s adjusted tax basis in such WGP common units. The amount and effect of any gain that may be recognized by holders of WES common units will depend on such unitholder’s particular situation, including the ability of such unitholder to utilize any suspended passive losses.

For additional information, please read “Material U.S. Federal Income Tax Consequences of the Merger—Tax Consequences of the Merger to WES and WES Common Unitholders.”

Risks Related to WES’s Business

You should read and consider the risk factors specific to WES’s business that will also affect WGP after completion of the Merger. These risks are described in WES’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017, as updated by any subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, all of which are filed with the SEC and incorporated by reference into this proxy statement/prospectus. See the section titled “Where You Can Find More Information” for the location of information incorporated by reference into this proxy statement/prospectus.

Risks Related to WGP’s Business

You should read and consider the risk factors specific to WGP’s business that will also affect WGP after completion of the Merger. These risks are described in WGP’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017, as updated by any subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, all of which are filed with the SEC and incorporated by reference into this proxy statement/prospectus. See the section titled “Where You Can Find More Information” for the location of information incorporated by reference into this proxy statement/prospectus.

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Tax Risks Related to Owning Common Units in WGP Following the Merger

Following the Merger, in addition to the risks described above, holders of WGP common units will continue to be subject to the risks to which holders of WGP common units are currently subject, which are described in WGP’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017, as updated by any subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, all of which are filed with the SEC and incorporated by reference into this proxy statement/prospectus. See “Where You Can Find More Information” for the location of information incorporated by reference in this proxy statement/prospectus.

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

We have made forward-looking statements concerning the Merger and our operations, economic performance and financial condition in this proxy statement/prospectus and the documents incorporated herein by reference. These forward-looking statements include statements preceded by, followed by or that otherwise include the words “believes,” “expects,” “anticipates,” “intends,” “estimates,” “projects,” “target,” “goal,” “plans,” “objective,” “should” or similar expressions or variations on such expressions. Forward-looking statements are also found under “The Merger—Unaudited Financial Projections.” These statements discuss future expectations, contain projections of results of operations or financial condition or include other “forward-looking” information. Although WGP, WGP GP, WES and WES GP believe that the expectations reflected in such forward-looking statements are reasonable, neither WGP, WGP GP, WES nor WES GP can give any assurance that such expectations will prove to have been correct. These forward-looking statements involve risks and uncertainties. Important factors that could cause actual results to differ materially from expectations include, but are not limited to, the following:

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The risk factors and other factors noted throughout or incorporated by reference in this proxy statement/prospectus could cause actual results to differ materially from those contained in any forward-looking statement. Except as required by law, WGP and WES undertake no obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

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THE PARTIES

Western Gas Equity Partners, LP and Western Gas Equity Holdings, LLC

WGP is a Delaware MLP with common units traded on the NYSE under the symbol “WGP.” WGP was formed by APC in September 2012 and its sole assets are the general partner interest in WES (held indirectly through WES GP), as well as the IDRs and WES common units. WGP is managed by its general partner, WGP GP, a Delaware limited liability company that is owned and controlled by APC. Merger Sub is a Delaware limited liability company and a wholly owned subsidiary of WGP.

The address of WGP’s and WGP GP’s principal executive offices is 1201 Lake Robbins Drive, The Woodlands, Texas 77380, and the telephone number at this address is (832) 636-6000.

Western Gas Partners, LP and Western Gas Holdings, LLC

WES is a Delaware MLP with common units traded on the NYSE under the symbol “WES.” WES is managed by its general partner, WES GP, a Delaware limited liability company that is owned and controlled by WGP. WES is engaged in the business of gathering, compressing, treating, processing and transporting natural gas; gathering, stabilizing and transporting condensate, NGLs and crude oil; and gathering and disposing of produced water. In addition, in its capacity as a processor of natural gas, WES also buys and sells natural gas, NGLs and condensate on behalf of itself and as agent for its customers under certain of its contracts. WES provides these midstream services for APC, as well as for third-party producers and customers.

The address of WES’s and WES GP’s principal executive offices is 1201 Lake Robbins Drive, The Woodlands, Texas 77380, and the telephone number at this address is (832) 636-6000.

Clarity Merger Sub, LLC

Merger Sub is a Delaware limited liability company and a wholly owned subsidiary of WGP. Merger Sub was formed on November 5, 2018 solely for the purpose of consummating the Merger and has no operating assets. Merger Sub has not carried on any activities to date, except for activities incidental to its formation and activities undertaken in connection with the transactions contemplated by the Merger Agreement. At the effective time, Merger Sub will merge with and into WES, with WES as the surviving entity.

The address of Merger Sub’s principal executive offices is 1201 Lake Robbins Drive, The Woodlands, Texas 77380, and the telephone number at this address is (832) 636-6000.

Parties to the Pre-Merger Transactions

Certain other affiliates of WGP and WES, including APC and certain of its subsidiaries, are also parties to the Merger Agreement. Although not direct parties to the Merger, such other parties to the Merger Agreement are parties to the various related transactions that will take place immediately prior to the effective time, including the Contribution and the Sale. For additional discussion of such parties and transactions, please see “The Merger—Pre-Merger Transactions.”

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THE SPECIAL MEETING

WES is providing this proxy statement/prospectus to its unitholders in connection with the solicitation of proxies to be voted at the special meeting of unitholders that WES has called for, among other things, the purpose of holding a vote upon a proposal to approve the Merger Agreement and the transactions contemplated thereby, including the Merger, and any adjournment thereof. This proxy statement/prospectus constitutes a proxy statement of WES in connection with the special meeting of WES unitholders and a prospectus for WGP in connection with the issuance by WGP of its common units as Merger Consideration. This proxy statement/prospectus is first being mailed to WES’s unitholders on or about January 28, 2019, and provides WES unitholders with the information they need to know to be able to vote or instruct their vote to be cast at the special meeting of WES unitholders.

Date, Time and Place

The special meeting will be held at 1201 Lake Robbins Drive, The Woodlands, Texas 77380, on February 27, 2019, at 8:00 a.m., local time.

Purpose

At the special meeting, WES unitholders will be asked to vote solely on the following proposals:

Recommendation of the WES GP Board

The WES GP Board recommends, based in part on the recommendation and special approval of the WES Special Committee, that unitholders of WES vote:

The WES GP Board has unanimously, in good faith, determined that the Merger Agreement and the transactions contemplated thereby, including the Merger, are advisable, fair and reasonable to and in the best interests of WES and its limited partners, following the recommendation of the WES Special Committee that the Merger Agreement and the transactions contemplated thereby, including the Merger, are advisable, fair and reasonable to and in the best interests of WES and its limited partners (excluding WGP, APC and their respective affiliates), and each of the WES GP Board and the WES Special Committee has unanimously, in good faith, approved the Merger Agreement and the transactions contemplated thereby, including the Merger. The WES GP Board has directed that the Merger Agreement be submitted to a vote of the WES unitholders and resolved to recommend approval of the Merger Agreement and the transactions contemplated thereby, including the Merger, to the WES unitholders. See “The Merger—Recommendation of the WES GP Board; Reasons for the Merger.”

In considering the recommendation of the WES GP Board with respect to the Merger Agreement and the transactions contemplated thereby, including the Merger, you should be aware that some or all of WES GP’s directors and executive officers may have interests that are different from, or in addition to, the interests of WES unitholders more generally. See “The Merger—Interests of Directors and Executive Officers of WES GP in the Merger.”

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Record Date; Outstanding Units; Units Entitled to Vote

The record date for the special meeting is January 14, 2019. Only WES common and Class C unitholders of record at the close of business on the record date will be entitled to receive notice of and to vote at the special meeting or any adjournment of the meeting.

As of the close of business on the record date of January 14, 2019, there were approximately 152,609,285 WES common units and 14,372,665 Class C units outstanding and entitled to vote at the meeting (including an aggregate of 52,143,426 WES common units and 14,372,665 Class C units held by APC, WGP and their respective affiliates). Each WES common and Class C unit is entitled to one vote.

Pursuant to the WES Partnership Agreement, if at any time any person or group (other than WES GP and its affiliates, including APC and WGP) beneficially owns 20% or more of any class of WES units, such person or group loses voting rights on all of its units and such units will not be considered “outstanding.” This loss of voting rights does not apply to (i) any person or group who acquired 20% or more of any class of WES units from WES GP or its affiliates, (ii) any person or group who directly or indirectly acquired 20% or more of any class of WES units from that person or group described in clause (i) provided WES GP notified such transferee that such loss of voting rights did not apply, or (iii) any person or group who acquired 20% or more of any class of units issued by WES with the prior approval of the WES GP Board.

A complete list of WES unitholders entitled to vote at the special meeting will be available for inspection at WES’s principal executive offices at 1201 Lake Robbins Drive, The Woodlands, Texas 77380 during regular business hours for a period of no less than 10 days before the special meeting and at the place of the special meeting during the meeting.

Quorum

A quorum of WES unitholders represented in person or by proxy at the special meeting is required to vote on the merger proposal at the special meeting, but not to vote on approval of any adjournment of the meeting. The holders of at least a majority of the outstanding WES common units and Class C units taken as a single class must be represented in person or by proxy at the meeting in order to constitute a quorum. Any abstentions and broker non-votes will be counted in determining whether a quorum is present at the special meeting.

Required Vote

To approve the Merger Agreement and the transactions contemplated thereby, including the Merger, the holders of at least a majority of the outstanding WES common units and Class C units voting as a single class must vote in favor of such approval. WES cannot complete the Merger unless its unitholders approve the Merger Agreement and the transactions contemplated thereby, including the Merger. Because approval requires the affirmative vote of at least a majority of the outstanding WES common and Class C units voting as a single class, a WES unitholder’s failure to vote, an abstention from voting or a broker non-vote will have the same effect as a vote “AGAINST” approval of the merger proposal.

If a quorum is present at the special meeting, to approve the adjournment of the meeting, if necessary, to solicit additional proxies if there are not sufficient votes to approve the Merger Agreement and the transactions contemplated thereby, including the Merger, at the time of the special meeting, holders of at least a majority of the outstanding WES common units and Class C units voting as a single class must vote in favor of the adjournment proposal. Therefore, if a quorum is present at the meeting, abstentions, broker non-votes and a WES common unitholder’s failure to vote will have the same effect as a vote “AGAINST” approval of the adjournment proposal. If a quorum is not present at the special meeting, to approve the adjournment of the meeting, holders of at least a majority of the outstanding WES common and Class C units, voting as a single class, entitled to vote and represented thereat either in person or by proxy must vote in favor of the adjournment

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proposal. Therefore, if a quorum is not present, abstentions and broker non-votes will have the same effect as a vote “AGAINST” approval of the adjournment proposal, but a WES unitholder’s failure to vote will have no effect on the outcome of the adjournment proposal. In addition, the WES Partnership Agreement also allows WES GP to adjourn the meeting from time to time without the approval of WES unitholders.

Unit Ownership of and Voting by WES GP’s and WGP GP’s Directors, Executive Officers and Affiliates

As of January 22, 2019, WES GP’s directors and executive officers and their affiliates (excluding APC, WGP and their subsidiaries) beneficially owned and had the right to vote 81,134 WES units at the special meeting, which represent 0.049% of the WES units entitled to vote at the special meeting. Additionally, WGP GP’s directors and executive officers and their affiliates (excluding APC, WGP and their subsidiaries) beneficially owned and had the right to vote 19,732 WES units at the special meeting, which represent 0.012% of the WES units entitled to vote at the special meeting. It is expected that WES GP’s and WGP GP’s directors and executive officers and their affiliates will vote their WES common units “FOR” the approval of the Merger Agreement and the transactions contemplated thereby, including the Merger, although none of them has entered into any agreement requiring them to do so.

Additionally, pursuant to the Merger Agreement, WGP and APC have each agreed to vote all of the limited partner interests in WES then owned beneficially or of record by them or their respective subsidiaries in favor of the approval of the Merger Agreement, the transactions contemplated thereby, including the Merger, and any actions required in furtherance thereof, which includes, if necessary, the adjournment proposal. As of November 7, 2018, WGP directly or indirectly owned 50,132,046 WES common units, representing approximately 29.6% of the limited partner interests in WES entitled to vote at the special meeting, and APC, through subsidiaries other than WGP and WES GP, indirectly owned 2,011,380 WES common units and 14,045,429 Class C units, representing in the aggregate approximately 9.5% of the limited partner interests in WES entitled to vote at the special meeting.

Voting of Units by Holders of Record

If you are entitled to vote at the special meeting and hold your WES units in your own name, you can submit a proxy or vote in person by completing a ballot at the special meeting. However, WES encourages you to submit a proxy before the special meeting even if you plan to attend the special meeting in order to ensure that your WES units are voted. A proxy is a legal designation of another person to vote your WES units on your behalf. If you hold units in your own name, you may submit a proxy for your WES units by:

When a unitholder submits a proxy by telephone or through the Internet, his or her proxy is recorded immediately. WES encourages its unitholders to submit their proxies using these methods whenever possible. If you submit a proxy by telephone or the Internet, please do not return your proxy card by mail.

All WES units represented by each properly executed and valid proxy received before the special meeting will be voted in accordance with the instructions given on the proxy. If a WES unitholder executes a proxy card without giving instructions, the WES units represented by that proxy card will be voted as the WES GP Board recommends, which is:

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Your vote is important. Accordingly, please submit your proxy by telephone, through the Internet or by mail, whether or not you plan to attend the meeting in person. Proxies must be received by 11:59 p.m., Eastern Time, on February 26, 2019. However, if the special meeting is adjourned to solicit additional proxies, the deadline may be extended.

Voting of Units Held in Street Name

If your WES units are held in an account at a bank, broker or through another nominee, you must instruct the bank, broker or other nominee on how to vote your WES units by following the instructions that the bank, broker or other nominee provided to you with these proxy materials. Most brokers offer the ability for unitholders to submit voting instructions by mail by completing a voting instruction card, by telephone and via the Internet.

If you do not provide voting instructions to your broker, your WES units will not be voted on any proposal on which your broker does not have discretionary authority to vote. This is referred to in this proxy statement/prospectus and in general as a broker non-vote. In these cases, the bank, broker or other nominee can register your WES units as being present at the special meeting for purposes of determining a quorum, but will not be able to vote your WES units on those matters for which specific authorization is required. Under the current rules of the NYSE, brokers do not have discretionary authority to vote on either of the proposals, including the merger proposal. A broker non-vote of a WES unit will have the same effect as a vote “AGAINST” the merger proposal and the adjournment proposal.

If you hold WES units through a bank, broker or other nominee and wish to vote your WES units in person at the special meeting, you must obtain a proxy from your bank, broker or other nominee and present it to the inspector of election with your ballot when you vote at the special meeting.

Revocability of Proxies; Changing Your Vote

You may revoke your proxy and/or change your voting instructions at any time before your proxy is voted at the special meeting. If you are a WES unitholder of record, you can do this by:

If you hold your WES units through a bank, broker or other nominee, you must follow the directions you receive from your bank, broker or other nominee in order to revoke your proxy or change your voting instructions.

Solicitation of Proxies

This proxy statement/prospectus is furnished in connection with the solicitation of proxies by the WES GP Board to be voted at the special meeting. WES will bear all costs and expenses in connection with the solicitation of proxies. WES has engaged Morrow Sodali LLC to assist in the solicitation of proxies for the meeting and

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WES estimates it will pay Morrow Sodali LLC a fee of approximately $12,500 for these services. WES has also agreed to reimburse Morrow Sodali LLC for reasonable out-of-pocket expenses and disbursements incurred in connection with the proxy solicitation and to indemnify Morrow Sodali LLC against certain losses, costs and expenses. In addition, WES may reimburse brokerage firms and other persons representing beneficial owners of WES units for their reasonable expenses in forwarding solicitation materials to such beneficial owners. Proxies may also be solicited by certain of WES GP’s directors, officers and employees by telephone, electronic mail, letter, facsimile or in person, but no additional compensation will be paid to them.

Unitholders Should Not Send Unit Certificates with Their Proxies

WES unitholders should not send in their unit certificates at this time. After completion of the Merger, WGP’s exchange agent will send you a letter of transmittal and instructions for exchanging your WES common units for the Merger Consideration.

No Other Business

Under the WES Partnership Agreement, the business to be conducted at the special meeting will be limited to the purposes stated in the notice to WES unitholders provided with this proxy statement/prospectus.

Adjournments

Adjournments may be made for the purpose of, among other things, soliciting additional proxies. If a quorum exists, an adjournment may be made from time to time with approval of the holders of at least a majority of the outstanding WES common and Class C units voting as a single class. If a quorum does not exist, an adjournment may be made from time to time with the approval of the holders of at least a majority of the WES common and Class C units, voting as a single class, entitled to vote at such meeting and represented thereat either in person or by proxy. WES is not required to notify unitholders of any adjournment of 45 days or less if the time and place of the adjourned meeting are announced at the meeting at which the adjournment is taken, unless after the adjournment a new record date is fixed for the adjourned meeting. At any adjourned meeting, WES may transact any business that it might have transacted at the original meeting, provided that a quorum is present at such adjourned meeting. Proxies submitted by WES unitholders for use at the special meeting will be used at any adjournment of the meeting. References to the special meeting in this proxy statement/prospectus are to such special meeting as adjourned.

Assistance

If you need assistance in completing your proxy card or have questions regarding the special meeting, please contact Morrow Sodali LLC toll-free at 800-662-5200 (banks and brokers call collect at 203-658-9400).

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THE MERGER

This section of the proxy statement/prospectus describes the material aspects of the proposed Merger. This section may not contain all of the information that is important to you. You should carefully read this entire proxy statement/prospectus and the documents incorporated herein by reference, including the full text of the Merger Agreement, for a more complete understanding of the Merger. A copy of the Merger Agreement is attached as Annex A hereto. In addition, important business and financial information about each of WGP and WES is included in or incorporated into this proxy statement/prospectus by reference. See “Where You Can Find More Information.”

Effect of the Merger

Subject to the terms and conditions of the Merger Agreement and in accordance with Delaware law, the Merger Agreement provides for the merger of Merger Sub with and into WES. WES, which is sometimes referred to following the Merger as the surviving entity, will survive the Merger, and the separate limited liability company existence of Merger Sub will cease. As a result of the transactions contemplated by the Merger Agreement, including the Merger, WGP will acquire substantially all of the outstanding WES common units that WGP and its subsidiaries do not already own, with APC indirectly owning the remaining WES common units. After the completion of the Merger, the certificate of limited partnership of WES in effect immediately prior to the effective time will be the certificate of limited partnership of the surviving entity, until amended in accordance with its terms and applicable law. In addition, immediately prior to the effective time, the WES Partnership Agreement will be amended and restated in the form of the Third Amended and Restated Limited Partnership Agreement of WES attached as Annex C to this proxy statement/prospectus (the “WES LPA amendment”) to, among other things, reflect the conversion of WES’s general partner units into a non-economic general partner interest in WES and WES common units and the conversion of the IDRs and Class C units into WES common units. At the effective time, the WES Partnership Agreement, as amended and restated in the form of the WES LPA amendment, will remain unchanged and will be the agreement of limited partnership of the surviving entity from and after the effective time, until amended in accordance with its terms and applicable law.

The Merger Agreement provides that, at the effective time, each WES common unit issued and outstanding as of immediately prior to the effective time (other than WES common units owned by WGP or subsidiaries of WGP or WES GP, and the WES common units to be issued in the Contribution) will be converted into the right to receive 1.525 WGP common units. WGP will not issue any fractional units in the Merger. Instead, all fractional WGP common units that a holder of WES common units would have been entitled to receive in the Merger will be aggregated and then, if a fractional WGP common unit results from that aggregation, be rounded up to the nearest whole WGP common unit. Each WES common unit owned by WGP and its subsidiaries and issued and outstanding immediately prior to the effective time (including any WES common units issued in connection with the pre-Merger transactions described below) will remain unchanged and remain outstanding.

Because the exchange ratio was fixed at the time the Merger Agreement was executed and because the market value of WGP common units and WES common units will fluctuate prior to the consummation of the Merger, WES common unitholders cannot be sure of the value of the Merger Consideration they will receive relative to the value of WES common units that they are exchanging. For example, decreases in the market value of WGP common units will negatively affect the value of the Merger Consideration that WES common unitholders receive, and increases in the market value of WES common units may mean that the Merger Consideration that such unitholders receive will be worth less than the market value of the WES common units that they are exchanging. See “Risk Factors—Risks Related to the Merger.”

If, as a WES GP employee or other service provider, you received WES phantom units, and if the Merger is completed, each unvested award of WES phantom units will, as of the effective time, be converted into the right to receive a phantom unit or other comparable equity award with respect to WGP common units on substantially

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the same terms and conditions as were applicable to the corresponding WES phantom unit award (including with respect to vesting), except that the number of WGP common units covered by such comparable award will be equal to the number of WES common units covered by the corresponding WES phantom unit award multiplied by the exchange ratio, rounded up to the nearest whole WGP common unit.

Pre-Merger Transactions

Subject to the conditions to the Merger being satisfied or waived (other than conditions that by their nature are to be satisfied at closing, but subject to the satisfaction or waiver of those conditions), APC, WGP and WES will, and will cause their respective affiliates to, cause the following transactions (collectively, the “pre-Merger transactions”), among others, to occur immediately prior to the effective time in the order set forth below:

The interests to be acquired by the Recipient Parties and WES in the pre-Merger transactions are referred to herein as the “Dropdown Assets.” The WES common units to be issued in connection with the pre-Merger transactions will be issued after the record date for the special meeting and therefore will not be entitled to vote at the special meeting. The 45,760,201 WES common units to be issued to the Contributing Parties, less 6,375,284 WES common units to be retained by WGRAH, will be converted into the right to receive an aggregate of 55,360,984 WGP common units upon the consummation of the Merger.

In connection with the cash consideration referred to above, WES has obtained, subject to customary closing conditions, committed debt financing for $2.0 billion from Barclays Bank PLC.

Background of the Merger

Since WES’s initial public offering in 2008, the board of directors and senior management of WES GP have regularly reviewed and discussed WES’s strategic objectives as well as opportunities to create or enhance value for WES’s unitholders. As a result of the drop in commodity prices in 2014-2016, these discussions have increasingly focused on how to best position WES for future growth, including through acquisitions, organic growth projects, operational improvements or other strategic alternatives. Given WES’s structure as an MLP, these deliberations have always been tied to discussions regarding WES’s access to, and cost of, capital.

Beginning in the second quarter of 2017, management began to examine in a more detailed way a variety of strategic transactions that could reduce WES’s cost of capital, primarily through the reduction or elimination of the burden of the IDRs. Several of WES’s peer MLPs had completed or announced simplification transactions, and inquiries from WES’s investors regarding when, and how, WES might mitigate or eliminate the burden of the IDRs were becoming more frequent.

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On August 10, 2017, at a regularly scheduled meeting of the WES GP Board and the WGP GP Board, management explained that WES’s “GP take” (distributions to WES GP on its general partner units and the IDRs) was one of the highest among midstream MLPs, and estimated that the IDRs added approximately 3.5% to WES’s cost of equity capital. Management also provided an overview of recent simplification transactions by other MLPs, and discussed the options available to WES for mitigating the impact of the IDRs on WES’s cost of capital, including a “reset” of WES’s incentive distribution tiers, a buyout of the IDRs by WES in exchange for additional WES common units, and a consolidation of WES and WGP, as well as some of the considerations and potential benefits of each option.

At the regularly scheduled meeting of the WES GP Board and the WGP GP Board on February 15, 2018, management noted that several additional IDR restructuring transactions had been announced since the August 2017 board meeting. Management also explained that investor sentiment towards MLPs with incentive distribution rights had continued to become less favorable since August 2017, and that certain equity investors had indicated that they would not take an ownership position (or increase their position) in WES until the IDRs were addressed. As a result, management reported that although WES’s growth forecast through 2019 was strong, and therefore management expected that WES could continue to grow its distributions without engaging in a simplification transaction, a multi-disciplinary project team would be created to thoroughly examine the business, financial, tax and accounting implications of each of the various options for mitigating or eliminating the burden of the IDRs, as well as the potential effects that each option would have on WES’s unitholders.

Shortly thereafter, Barclays Capital Inc. (“Barclays”) began assisting WES GP’s management with evaluating the various alternatives and determining which transaction would be most beneficial to all of WES’s stakeholders.

From February through August 2018, the project team met numerous times to review and discuss the benefits and considerations associated with each of the options, including with respect to tax implications, trading liquidity, distribution coverage and growth, accretion and leverage. The analysis also considered the impacts of a simultaneous acquisition of midstream assets from APC.

On May 8, 2018, at a regularly scheduled meeting of the WES GP Board and the WGP GP Board, management provided an update on its evaluation of the various options, which included (i) a “reset” or “buydown” of the IDRs, (ii) the conversion of pro forma WGP to a corporation (without simplification), (iii) the acquisition of WES by WGP, and (iv) the acquisition of WGP by WES. Management explained that the MLP equity markets remained challenging, especially for MLPs with incentive distribution rights, and reviewed the additional simplification transactions that had been announced since the last board meeting. Management then discussed each of the options in more detail, explaining that a “reset” or “buydown” of the IDRs had been largely eliminated from consideration because these alternatives would not provide a permanent solution for WES’s increasing cost of capital. Further, the conversion of WGP into a corporation and the acquisition of WGP by WES would have significant adverse tax consequences. As a result, management explained that it had reached the conclusion that the acquisition by WGP of all of the publicly traded WES common units in exchange for WGP common units, in conjunction with the elimination of the IDRs and a significant acquisition by WES of midstream assets from APC, would likely be the most favorable transaction for all stakeholders, including WES’s unitholders, WGP’s unitholders and APC. Management stated that it had reached this conclusion based on a variety of factors, including the potential tax implications and the desirability of avoiding a distribution cut for WES’s unitholders. In addition, the consolidation of WES and WGP into a single, much larger publicly traded company would significantly enhance the trading liquidity of the common units of the resulting entity. Management also provided an overview of the expected simplification process and the related timing of a potential transaction. Management then reported that it was still analyzing the impact on any simplification transaction of three key variables: (i) the size of, and the amount of consideration paid for, the acquisition of midstream assets from APC, (ii) whether the resulting entity should remain an MLP, convert to a corporation or a limited liability company that elects to be taxed as a corporation, or utilize an “Up-C” structure (which includes an entity taxed as a partnership and an entity taxed as a corporation, with partnership securities exchangeable into

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securities of the corporation), and (iii) whether the WES Class C units should be converted into WES common units as part of the potential transaction.

Over the next several weeks, management continued to evaluate the various alternatives with the assistance of Barclays and V&E. Among other things, management reviewed the effects of the acquisition of a portion of APC’s midstream assets as compared to the acquisition of substantially all of APC’s midstream assets, the accretion of various acquisition price multiples, the forecasted trading liquidity of the resulting entity, and the tax effects of converting the resulting entity to a corporation or utilizing an “Up-C” structure. At various points, management met with representatives of APC to solicit their feedback on the proposed transactions.

At the regularly scheduled meeting of the WES GP Board and the WGP GP Board on August 15, 2018, management formally recommended the following series of transactions, subject to the approval of the WES GP Board, the WGP GP Board, and the respective special committees thereof:

Management explained that this series of transactions would be consummated more or less simultaneously, and that the benefits were expected to include the following:

Management did not make a recommendation or state its expectations with respect to the price to be paid by WES for the Dropdown Assets, or the premium to be paid to WES’s unitholders in the merger. Rather, management reviewed several sensitivity analyses which showed the accretion/dilution impact to WES’s estimated 2019 distribution per unit at a hypothetical range of acquisition multiples and unit price premiums. Management also reviewed an illustrative timeline for the announcement and closing of the potential transactions.

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Thereafter, Milton Carroll, as chairman of the WES Special Committee, informed Bracewell LLP (“Bracewell”) of the foregoing potential transactions and advised them that the WES Special Committee was prepared to engage Bracewell to assist the WES Special Committee in evaluating the potential transactions. Bracewell had previously represented the WES Special Committee in all related party transactions involving WES and APC which had been reviewed by the WES Special Committee. On August 21, 2018, the members of the WES Special Committee met with Bracewell representatives. Among other things, Bracewell’s engagement as counsel was confirmed, and Bracewell confirmed with each member of the WES Special Committee his independence as defined in the WES Partnership Agreement, discussed “Special Approval,” as defined in the WES Partnership Agreement, and reviewed the WES Special Committee’s duties and responsibilities applicable to the potential transactions. The WES Special Committee selected Bracewell because of its prior work for the WES Special Committee, its knowledge and familiarity with WES and the industry in which WES operates, its experience with mergers and acquisitions, including mergers and acquisitions involving MLPs, and its experience with MLPs generally, among other reasons. The WES Special Committee was also prepared to finalize the engagement of a financial advisor to assist the WES Special Committee in its deliberations.

By letter dated August 27, 2018, the WES Special Committee engaged Lazard as its financial advisor. The WES Special Committee engaged Lazard because of its qualifications, experience and reputation in investment banking and mergers and acquisitions, and its familiarity with WES and its business. The engagement letter was subsequently amended to clarify the scope of Lazard’s engagement.

Following the August 15, 2018 WES GP Board and WGP GP Board meetings, the WGP Special Committee considered the engagement of financial and legal advisors. After consideration of potential financial advisors and based on Citigroup Global Markets Inc.’s (“Citi”) familiarity with WGP and WES and Citi’s experience with public mergers and acquisitions, complex transactions involving publicly traded partnerships and representations of conflicts committees, the WGP Special Committee determined that Citi had the requisite experience to provide high-quality advice to the WGP Special Committee and subsequently engaged Citi as financial advisor to the WGP Special Committee. In connection with its engagement, Citi disclosed to the WGP Special Committee certain information regarding Citi’s material investment banking relationships with APC and certain of its affiliates. In addition, following consideration of potential legal advisors and based on Richards, Layton & Finger, P.A.’s (“RLF”) familiarity with WGP and WES and RLF’s experience with public mergers and acquisitions, complex transactions involving publicly traded partnerships and representations of conflicts committees, the WGP Special Committee determined that RLF had the requisite expertise to provide high-quality advice to the WGP Special Committee. The terms of the WGP Special Committee’s engagement with RLF were confirmed by a letter dated August 29, 2018.

On August 29, 2018, members of management met with the WGP Special Committee and its advisors to present them with the same overview of the proposed transactions, and anticipated timeline for considering the proposed transactions, that had been presented to the WES GP Board and the WGP GP Board at the August 15th board meetings. In addition, management informed the WGP Special Committee’s advisors that APC had indicated that it believed that 10x the 2019E Adjusted EBITDA of the Dropdown Assets would be an appropriate price for those assets.

Later on August 29, 2018, the WGP Special Committee held a meeting with its advisors. The WGP Special Committee and its advisors discussed their initial reaction to the presentation from management of WGP and WES and their preliminary observations regarding the proposed transactions.

Beginning on September 7, 2018, the WES Special Committee’s advisors and the WGP Special Committee’s advisors were provided with access to a “virtual data room” containing due diligence information regarding the Dropdown Assets. Due diligence of the Dropdown Assets began shortly thereafter, and additional due diligence information was posted to the virtual data room, as it became available and/or in response to requests from the advisors to the WES Special Committee and the WGP Special Committee (collectively, the “Special Committees”), until the Merger Agreement was signed on November 7, 2018.

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On September 11, 2018, members of management held a meeting with certain members of the WES Special Committee and representatives of Lazard and Bracewell to provide them with the same overview of the proposed transactions, and the same additional information, that had been provided to the WGP Special Committee’s advisors on August 29, 2018. At this meeting, management communicated APC’s belief that 10x the 2019E Adjusted EBITDA of the Dropdown Assets would be an appropriate price for those assets.

On September 12, 2018, management presented an overview of the Dropdown Assets to certain members of the Special Committees and their respective advisors. Representatives of Barclays, V&E and APC were also in attendance. Management discussed the potential risks to the Dropdown Assets and WES’s business associated with passage of Colorado ballot initiative 97 (the “Colorado Ballot Initiative”), which would lengthen the minimum setback for oil and gas wells to 2,500 feet, in the upcoming Colorado general election scheduled for November 6, 2018.

Later on September 12, 2018, the WGP Special Committee held a meeting with its advisors. The WGP Special Committee and its advisors discussed the proposed transactions and the potential risks associated with passage of the Colorado Ballot Initiative. The RLF representatives made a presentation about the duties and responsibilities of the WGP Special Committee in connection with the proposed transactions.

On September 21, 2018, the WGP Special Committee held a meeting with its advisors. At the WGP Special Committee’s request, Citi discussed with the WGP Special Committee certain MLP simplification trends and potential simplification alternatives. The WGP Special Committee discussed with its advisors the impact the Colorado Ballot Initiative could have on the valuation of the proposed transactions if it were to pass.

On September 25 and September 27, 2018, representatives of APC held conference calls with Bracewell and RLF to answer their initial questions and present additional information pertaining to environmental and regulatory due diligence conducted with respect to the Dropdown Assets. Representatives of Lazard and Citi also participated in the calls.

Also on September 27, 2018, an initial draft of the Merger Agreement, which had been prepared by management and V&E, was made available to the Special Committees and their advisors through the virtual data room. The draft Merger Agreement did not address the economic terms of the Contribution, the Sale or the Merger.

On September 28, 2018, following discussion among management and members of the WGP Special Committee, it was decided that the WGP Special Committee would not be asked to make a recommendation regarding the proposed transaction to the WGP GP Board until at least November 7, 2018, at which time the parties would know if the Colorado Ballot Initiative had passed.

On September 30, 2018, the WES GP Board and the WGP GP Board adopted, by unanimous written consent, resolutions authorizing the WES Special Committee and the WGP Special Committee, respectively, to:

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In addition, among other things, the WES GP Board and the WGP GP Board (i) confirmed the authorization of the WES Special Committee and the WGP Special Committee, respectively, to engage such legal, financial and other advisors as each committee deemed necessary or appropriate, and (ii) directed the officers of WES GP and WGP GP, respectively, to assist each committee in any manner requested by such committee.

By letter dated October 1, 2018, the WES Special Committee engaged Morris, Nichols, Arsht & Tunnell LLP (“Morris Nichols”) to act as its special Delaware counsel in connection with the potential transactions. Bracewell shared and discussed the initial draft Merger Agreement with Morris Nichols.

On October 5, 2018, RLF, at the direction of the WGP Special Committee, submitted initial comments to the draft of the Merger Agreement to V&E and Bracewell. The principal issues raised were (i) the scope of WES’s representations and warranties, (ii) the scope of the representations and warranties regarding the Dropdown Assets, and (iii) the scope of the authority of the WGP Special Committee to approve amendments and consents under, or determinations to be made with respect to, the Merger Agreement.

On October 8, 2018, the WES Special Committee met with Bracewell to discuss the previously circulated draft Merger Agreement and hear recommendations with respect thereto. The WES Special Committee then instructed Bracewell to respond to the draft Merger Agreement. On October 9, 2018, Bracewell delivered a revised version of the Merger Agreement on behalf of the WES Special Committee to RLF and V&E, in which the principal issues raised were (i) the scope of the representations regarding the Dropdown Assets, (ii) the inclusion of an additional requirement that the Merger receive the approval of a majority of the WES unitholders unaffiliated with WGP, APC or their respective affiliates, (iii) the inclusion of provisions allowing the WES Special Committee to make a change in recommendation to WES unitholders with respect to the proposed transactions, and (iv) the scope of the authority of the WES Special Committee to approve amendments and consents under, or determinations to be made with respect to, the Merger Agreement.

On October 16, 2018, the “Project Clarity Forecast Model,” consisting of standalone forecasts for WES, WGP and the Dropdown Assets through 2021, as well as a pro forma combined forecast through 2021, and the “Project Clarity Asset Area Forecast,” consisting of forecasts by asset and/or geographic area for WES through 2021 and the Dropdown Assets through 2023, were made available to the Special Committees and their respective advisors through the virtual data room. Also on this date, APC communicated to the Special Committees’ financial advisors that APC would be willing to sell the Dropdown Assets at a price of $4.1 billion, which represented a 9.75x multiple of the 2019E Adjusted EBITDA.

On October 23, 2018, a revised draft of the Merger Agreement was made available to the Special Committees and their respective advisors through the virtual data room. The principal updates to the revised Merger Agreement included (i) an expansion of the representations and warranties made by the parties, and (ii) the addition of provisions allowing the WES Special Committee to make a change in recommendation to WES’s unitholders under certain circumstances. The revised draft rejected the WES Special Committee’s request that the Merger receive approval of a majority of the WES unitholders that are not affiliated with WES, WGP or APC. The revised draft also rejected the requests by the WES Special Committee and the WGP Special Committee that the Special Committees must approve amendments, consents or determinations under the Merger Agreement.

Also on October 23, 2018, members of management held a conference call with Lazard and Citi to discuss management’s financial models, which had been provided during the previous week. Representatives of V&E, RLF and Bracewell also participated in the call.

On October 24, 2018, an updated Project Clarity Forecast Model was made available to the Special Committees and their respective advisors through the virtual data room.

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On October 26, 2018, the WGP Special Committee held a meeting with its advisors. At the WGP Special Committee’s request, Citi discussed with the WGP Special Committee certain preliminary financial aspects of the proposed transactions. RLF summarized the draft Merger Agreement received on October 23, 2018 and the open issues therein. The WGP Special Committee discussed making a recommendation to the WGP GP Board regarding a proposed exchange ratio of WGP common units for WES common units in the Merger and expressly conditioning any such exchange ratio proposal on the outcome of the Colorado Ballot Initiative such that it was understood that the proposal could be revoked if the Colorado Ballot Initiative passed.

Later on October 26, 2018, representatives of Bracewell and RLF discussed the scope of the authority of the respective Special Committees to approve amendments and consents under, or determinations to be made with respect to, the Merger Agreement.

RLF and Bracewell, on behalf of the WGP Special Committee and the WES Special Committee, respectively, submitted comments to the October 23 draft of the Merger Agreement on October 26 and October 29, 2018, respectively. The principal issues raised in the comments submitted on behalf of the WGP Special Committee were (i) narrowing provisions allowing the WES Special Committee to make a change in recommendation to WES’s unitholders and (ii) the addition of a termination fee payable by WES if the WES Special Committee made a change in recommendation. The principal issues raised in the comments submitted on behalf of the WES Special Committee were (i) elimination of a proposed obligation that WES reimburse WGP for WGP’s expenses in connection with the transaction if WES unitholders do not approve the proposed transactions, and (ii) provisions providing the Special Committees with the authority to approve amendments and consents under, or determinations with respect to, the Merger Agreement.

On October 30, 2018, the WGP Special Committee held a meeting with its advisors to discuss the proposed transactions. At the WGP Special Committee’s request, Citi updated the WGP Special Committee regarding certain preliminary financial aspects of the proposed transactions. RLF provided an update on legal issues associated with the proposed transactions. Following discussion and consideration, the WGP Special Committee concluded that it would recommend to the WGP GP Board that the WGP GP Board make a proposal to the WES Special Committee and prepared a draft proposal letter to share with the WGP GP Board. The material terms of the proposal letter (the “Initial WGP Proposal”) included the following:

The proposal letter was expressly conditioned upon certain key assumptions, including (i) that WES would pay aggregate consideration with a value of no more than $4.115 billion to APC for the Dropdown Assets, which consideration would be paid 50% in cash or the assumption of debt and 50% through the issuance of WES common units to APC, (ii) that the Colorado Ballot Initiative would not be approved in Colorado’s general election on November 6, 2018, (iii) that WES would have received a fully underwritten commitment to fund the cash portion of the consideration for the Dropdown Assets by the time the definitive transaction documents were signed, and (iv) that all of the Class C units held by APC would be converted into WES common units on a one-for-one basis immediately before the closing of the proposed transactions.

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Later on October 30, 2018, the WGP GP Board held a special meeting at which all directors, as well as Jaime R. Casas and Philip H. Peacock, were present. Thomas Hix, as chairman of the WGP Special Committee, reported on the recent deliberations and activities of the WGP Special Committee and its advisors regarding the proposed transactions. The WGP Special Committee recommended that the WGP GP Board approve a proposal to the WES Special Committee with respect to the proposed transactions as set forth, and on the terms more specifically described, in the draft proposal letter which had been previously distributed to the members of the WGP GP Board. Following extensive discussion, the WGP GP Board approved the making of the Initial WGP Proposal to acquire WES on the terms recommended by the WGP Special Committee.

Later on October 30, 2018, Robert G. Gwin, on behalf of the WGP GP Board, delivered a proposal letter to Milton Carroll, as chairman of the WES Special Committee, which set forth the terms of the Initial WGP Proposal.

On November 1, 2018, the WES Special Committee met with its advisors to evaluate the Initial WGP Proposal. The structure and initial terms of the transactions contemplated by the draft Merger Agreement were discussed, and Lazard presented its preliminary financial analyses, including (i) standalone valuation analyses of WES and WGP utilizing (a) dividend discount model analyses, (b) comparable company analyses, and (c) a precedent transaction analysis (with respect to WES only), (ii) standalone valuation analyses of the Dropdown Assets utilizing (a) a discounted cash flow analysis, (b) a comparable company analysis, and (c) a precedent transaction analysis, and (iii) valuation analyses of the combined company after giving effect to the Merger and the pre-Merger transactions, utilizing (a) a financial impact (or “has/gets”) analysis, and (b) a relative implied exchange ratio analysis. During the presentation, the WES Special Committee asked, and Lazard representatives answered, questions with respect to Lazard’s preliminary financial analyses. Following further discussion, the WES Special Committee instructed its advisors as to responses with respect to the draft Merger Agreement and the Initial WGP Proposal.

Also on November 1, 2018, members of management held a call with members of the Special Committees and representatives of their advisors to discuss the Colorado Ballot Initiative, its prospects for passage, and APC’s and WES’s plans and financial forecasts following the election.

Later on November 1, 2018, representatives of Bracewell and RLF discussed the appropriateness and proposed amount of a termination fee payable by WES to WGP in certain events.

Between November 2 and November 7, 2018, representatives of APC, the WES Special Committee and the WGP Special Committee negotiated the remaining terms of the Merger Agreement.

On November 2, 2018, representatives of Lazard, on behalf of the WES Special Committee, communicated counterproposals to representatives of APC and Citi, respectively, that (i) the price for the Dropdown Assets be reduced to $3.7 billion and (ii) the exchange ratio be increased to 1.54 WGP common units for each WES common unit (other than WES common units owned by WGP or subsidiaries of WGP or WES GP and the WES common units to be issued in the Contribution) (the “WES Exchange Ratio Counterproposal”).

Also on November 2, 2018, the WGP Special Committee held a meeting with its advisors. Representatives of Citi updated the WGP Special Committee regarding recent conversations, on behalf of the WGP Special Committee, with Lazard regarding the Initial WGP Proposal and APC’s proposed purchase price for the Dropdown Assets. The WGP Special Committee and its advisors discussed the WES Special Committee’s anticipated counterproposal to APC of a $3.7 billion purchase price for the Dropdown Assets and the WGP Special Committee instructed representatives of Citi to communicate to Lazard that the WGP Special Committee would respond to the WES Special Committee’s proposed exchange ratio once the WES Special Committee had finalized negotiations with APC regarding the purchase price for the Dropdown Assets. Following the meeting, in accordance with the WGP Special Committee’s directives, representatives of Citi communicated the expected timing for the WGP Special Committee’s response to representatives of Lazard.

Later on November 2, 2018, following discussions between APC management and representatives of Lazard, APC agreed to lower its asking price for the Dropdown Assets to $4.015 billion, which represented a 9.52x multiple of the 2019E Adjusted EBITDA.

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On November 4, 2018, the WGP Special Committee held a meeting with its advisors to discuss the proposed transactions and the WES Exchange Ratio Counterproposal made on behalf of the WES Special Committee. Following consideration of the WES Exchange Ratio Counterproposal and discussion with its advisors, the WGP Special Committee determined that, assuming the Colorado Ballot Initiative did not pass, it planned to make a counterproposal to the WES Special Committee that WGP acquire the WES common units (other than WES common units owned by WGP or subsidiaries of WGP or WES GP and the WES common units to be issued in the Contribution) at an exchange ratio of 1.518 WGP common units for each WES common unit (the “WGP Counterproposal”) and the WGP Special Committee then directed Citi to communicate to Lazard the WGP Special Committee’s plan to make the WGP Counterproposal to the WES Special Committee. Following this meeting, in accordance with the WGP Special Committee’s directives, representatives of Citi communicated the planned WGP Counterproposal to representatives of Lazard.

Later on November 4, 2018, members of the WES GP Board and the WGP GP Board were informed of proposed management changes that would occur following the reorganization of WES and WGP as a result of the Merger.

On November 5, 2018, representatives of APC held a conference call with Bracewell to answer questions and present additional information pertaining to real property due diligence conducted with respect to the Dropdown Assets.

Also on November 5, 2018, representatives of RLF, Lazard, V&E and management of APC discussed the proposed terms of the draft Merger Agreement. During the call, representatives of APC agreed that the final Merger Agreement would require the approval of the Special Committees for any amendments, consents or determinations under the Merger Agreement. The parties continued to discuss the appropriateness and amount of a termination fee payable by WES to WGP in the event that the WES Special Committee were to make a change in recommendation and the parties discussed a potential termination fee of $60 million payable by WES to WGP in such circumstance.

On November 6, 2018, the WGP Special Committee held a meeting with its advisors. At the WGP Special Committee’s request, Citi updated the WGP Special Committee regarding certain preliminary financial aspects of the proposed transactions and its recent conversations, on behalf of the WGP Special Committee, with Lazard, on behalf of the WES Special Committee, regarding the WGP Counterproposal and certain related financial considerations. The RLF representatives provided an update on the terms of the revised draft of the Merger Agreement, including, among other things, the inclusion of a termination fee of $60 million payable by WES to WGP in the event of a WES change of recommendation resulting from an intervening event (as defined in the Merger Agreement).

Also on November 6, 2018, the WES Special Committee met with its advisors. The draft Merger Agreement, as further negotiated that day among legal representatives of APC and the Special Committees, was discussed. It was determined that, subject to reaching agreement on the exchange ratio, (i) the final Merger Agreement would not contain a condition that the Merger receive the approval of a majority of the WES unitholders unaffiliated with WGP, APC or their respective affiliates, (ii) the authority of the WES Special Committee with respect to the Merger Agreement would be strengthened, and (iii) a requirement that WES pay a cash termination fee of $60 million in the event that WGP were to terminate the Merger Agreement following a change in recommendation by the WES Special Committee in response to an intervening event would be included. Lazard then presented updates to its preliminary financial analyses and reviewed the negotiations held with representatives of APC and the WGP Special Committee, respectively, concerning the proposed consideration for the Dropdown Assets and the proposed exchange ratio. Following further discussion, the WES Special Committee instructed Lazard to continue negotiations with respect to the proposed exchange ratio.

Later on November 6, 2018, representatives of Lazard held discussions with representatives of APC and Citi, respectively, and communicated a counterproposal on behalf of the WES Special Committee that the

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exchange ratio be 1.525 WGP common units for each WES common unit (other than WES common units owned by WGP or subsidiaries of WGP or WES GP and the WES common units to be issued in the Contribution). Citi subsequently communicated the counterproposal to the WGP Special Committee.

Also on November 6, 2018, the Colorado Ballot Initiative was defeated in Colorado’s general election.

On November 7, 2018, the advisors of APC, WGP and WES held discussions with representatives of WES, WGP and APC to confirm the unit numbers that would, subject to the agreement of all parties on final terms, be included in the proposed final draft of the Merger Agreement based on the closing price of WES common units and WGP common units, respectively, on November 6, 2018.

Also on November 7, 2018, the WGP Special Committee held a meeting with its advisors. Prior to the meeting, substantially final versions of the Merger Agreement and other ancillary documents were distributed to the WGP Special Committee. At the WGP Special Committee’s request, Citi discussed with the WGP Special Committee certain financial aspects of the proposed transactions. RLF then provided the WGP Special Committee with an overview of various legal matters relating to the proposed transactions. Following discussion, the WGP Special Committee unanimously (i) determined in good faith that the proposed transactions, including the Merger Agreement and the transactions contemplated thereby, on the terms set forth in the Merger Agreement, are in the best interests of WGP and the holders of WGP common units (other than WGP GP and its controlling affiliates, including APC), (ii) approved the proposed transactions, including the Merger Agreement and the transactions contemplated thereby upon the terms and conditions set forth in the Merger Agreement, and (iii) resolved to recommend that the WGP GP Board approve the proposed transactions, including the Merger Agreement and the transactions contemplated thereby upon the terms and conditions set forth in the Merger Agreement.

Also on November 7, 2018, the WES Special Committee met with its advisors. At the meeting, and before Lazard representatives were present, Bracewell reminded the WES Special Committee members of their duties and responsibilities and the legal framework in which to consider the proposed transactions. Representatives of Lazard then joined the meeting, whereupon Bracewell representatives summarized the material terms of the Merger Agreement and noted any material changes made subsequent to the prior WES Special Committee meeting. Lazard presented its final financial analyses of the proposed transactions, noting that the materials and financial analyses were substantially equivalent to those previously presented to the WES Special Committee, updated for developments since the prior materials. Lazard also delivered its oral opinion to the WES Special Committee, which opinion was subsequently confirmed in writing, that, as of such date, and based upon and subject to the assumptions made, procedures followed, factors considered, and qualifications and limitations set forth in Lazard’s written opinion, the Merger Consideration to be received by the holders of WES common units (other than WES GP, WGP, APC and their respective affiliates) pursuant to the Merger Agreement after giving effect to the pre-Merger transactions, was fair, from a financial point of view, to such holders. Following review and discussion, the WES Special Committee unanimously (i) determined in good faith that the Merger Agreement and the transactions contemplated thereby, including the Merger, were advisable, fair and reasonable to, and in the best interests of, WES and its limited partners (excluding WGP, APC and their respective affiliates), (ii) approved the Merger Agreement and the transactions contemplated thereby, including the Merger, and (iii) resolved to recommend that the WES GP Board approve the Merger Agreement and the transactions contemplated thereby, including the Merger.

Later on November 7, 2018, the WGP GP Board held a special meeting at which all directors, as well as members of management, were present. Mr. Hix, as chairman of the WGP Special Committee, reported on the recent deliberations and activities of the WGP Special Committee and its advisors regarding the transactions described in the Merger Agreement. He also reported that the WGP Special Committee had, by unanimous vote, (i) determined in good faith that the proposed transactions, including the Merger Agreement and the transactions contemplated thereby, were in the best interests of WGP and the holders of WGP common units (excluding WGP GP and its controlling affiliates, including APC), and (ii) approved the proposed transactions, including the Merger Agreement and the transactions contemplated thereby, upon the terms and conditions set forth in the Merger Agreement. Following discussion, the WGP GP Board unanimously and in good faith (i) determined that the proposed transactions, including the Merger Agreement and the transactions contemplated thereby, were

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advisable, fair and reasonable to, and in the best interests of, WGP and its limited partners and (ii) approved and authorized the proposed transactions, including the Merger Agreement and the transactions contemplated thereby.

Later on November 7, 2018, following the WGP GP Board meeting, the WES GP Board held a special meeting at which all directors, as well as members of management, were present. Mr. Carroll, as chairman of the WES Special Committee, reported on the recent deliberations and activities of the WES Special Committee and its advisors regarding the transactions described in the Merger Agreement. He also reported on the WES Special Committee’s unanimous determinations regarding the Merger Agreement and the transactions contemplated thereby, including the Merger. Following discussion, the WES GP Board unanimously and in good faith (i) determined that the Merger Agreement and the transactions contemplated thereby, including the Merger, were advisable, fair and reasonable to, and in the best interests of, WES and its limited partners, (ii) approved the Merger Agreement and the transactions contemplated thereby, including the Merger, (iii) directed that the Merger Agreement be submitted to a vote of the limited partners of WES and (iv) resolved to recommend to the limited partners of WES the approval of the Merger Agreement and the transactions contemplated thereby, including the Merger.

In the evening of November 7, 2018, the Merger Agreement was executed, and early in the morning on November 8, 2018, WES and WGP issued a joint press release announcing the execution of the Merger Agreement.

Recommendation of the WES GP Board; Reasons for the Merger

By vote at a meeting of the WES Special Committee on November 7, 2018, the WES Special Committee unanimously, in good faith, (i) determined that the Merger Agreement and the transactions contemplated thereby, including the Merger, are advisable, fair and reasonable to, and in the best interests of, WES and its limited partners (excluding WGP, APC and their respective affiliates), (ii) approved the Merger Agreement and the transactions contemplated thereby, including the Merger, and (iii) resolved to recommend that the WES GP Board approve the Merger Agreement and the transactions contemplated thereby, including the Merger. In evaluating the Merger Agreement and the transactions contemplated thereby, the WES Special Committee considered information supplied by management of WES, WGP and APC, consulted with its legal and financial advisors, and considered a number of factors in reaching its determination, approval and recommendation. The WES Special Committee also consulted with its legal counsel regarding its duties and obligations.

Based on the WES Special Committee’s recommendation, the WES GP Board, by unanimous vote at a meeting held on November 7, 2018, in good faith, (i) determined that the Merger Agreement and the transactions contemplated thereby, including the Merger, are advisable, fair and reasonable to, and in the best interests of, WES and its limited partners, (ii) approved the Merger Agreement and the transactions contemplated thereby, including the Merger, (iii) directed that the Merger Agreement be submitted to a vote of the WES unitholders and (iv) resolved to recommend to the holders of WES units that they approve the Merger Agreement and the transactions contemplated thereby, including the Merger.

In the course of determining that the Merger Agreement and the transactions contemplated thereby, including the Merger, are advisable, fair and reasonable to, and in the best interests of, WES and its limited partners (excluding from this determination, in the case of the WES Special Committee, WGP, APC and their respective affiliates), the WES Special Committee and the WES GP Board considered, in addition to the matters discussed under “—Background of the Merger,” the following factors, which the WES Special Committee and the WES GP Board believe supports their decisions:

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In addition, the WES Special Committee and the WES GP Board considered a number of factors relating to the procedural safeguards involved in the negotiation of the Merger Agreement, including those discussed below, each of which supported their determinations with respect to the Merger:

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In the course of reaching the determinations and making the recommendation described above, the WES Special Committee and the WES GP Board also considered the following risks and potentially negative factors related to the Merger Agreement and the transactions contemplated thereby:

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The WES Special Committee and the WES GP Board considered all of the foregoing factors as a whole and, on balance, concluded that they supported a determination to approve the Merger Agreement and the transactions contemplated thereby, including the Merger. The foregoing discussion of the information and factors considered by the WES Special Committee and the WES GP Board includes the material factors, but is not exhaustive. In view of the wide variety of factors considered by the WES Special Committee and the WES GP Board in connection with their evaluation of the proposed Merger and the complexity of these matters, the WES Special Committee and the WES GP Board did not consider it practical to, and did not attempt to, quantify, rank or otherwise assign relative weights to the specific factors considered in reaching their decisions. The WES Special Committee and the WES GP Board evaluated the factors described above, among others, and in each case reached a consensus that the Merger Agreement and the transactions contemplated thereby, including the Merger, are advisable, fair and reasonable to, and in the best interests of, WES and its limited partners (excluding from this determination, in the case of the WES Special Committee, WGP, APC and their respective affiliates). In considering the factors described above, and any other factors, individual members of the WES Special Committee and the WES GP Board may have viewed factors differently or given weight or merit to different factors. The WES Special Committee approved the Merger Agreement and the transactions contemplated thereby, including the Merger, and made its recommendation to the WES GP Board based on the totality of the information presented to and considered by it. Similarly, the WES GP Board approved the Merger Agreement and the transactions contemplated thereby, including the Merger, and made its recommendation to WES unitholders based on the totality of the information presented to and considered by it.

In considering the approval of the Merger Agreement by the WES Special Committee and the WES GP Board, you should be aware that WES GP’s executive officers and directors have interests in the proposed Merger that may be different from, or in addition to, the interests of holders of WES common units generally. The WES Special Committee and the WES GP Board were aware of these interests and considered them when approving the Merger Agreement and the transactions contemplated thereby, including the Merger. See “The Merger—Interests of Directors and Executive Officers of WES GP in the Merger.”

The explanation of the reasoning of the WES Special Committee and the WES GP Board and certain other information presented in this section are forward-looking in nature and, therefore, the information should be read in light of the factors discussed in the section entitled “Cautionary Statement Regarding Forward-Looking Statements.”

The WES GP Board, based in part on the recommendation of the WES Special Committee, recommends that WES unitholders vote “FOR” the approval of the Merger Agreement and the transactions contemplated thereby, including the Merger, and “FOR” the proposal to approve the adjournment of the special meeting, if necessary, to solicit additional proxies if there are not sufficient votes to approve the Merger Agreement and the transactions contemplated thereby, including the Merger, at the time of the special meeting.

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Opinion of the Financial Advisor to the WES Special Committee

The WES Special Committee has retained Lazard to act as its financial advisor in connection with the Transactions. As part of this engagement, the WES Special Committee requested that Lazard evaluate the fairness, from a financial point of view, to the holders of WES common units (other than WES GP, WGP, APC and their respective affiliates) of the Merger Consideration to be received by such holders pursuant to the Merger Agreement, after giving effect to the pre-Merger transactions. At a meeting of the WES Special Committee held to approve the Transactions on November 7, 2018, Lazard rendered an oral opinion to the WES Special Committee, subsequently confirmed in writing, to the effect that, as of such date, and based upon and subject to the assumptions made, procedures followed, factors considered, and qualifications and limitations set forth in Lazard’s written opinion, the Merger Consideration to be received by the holders of WES common units (other than WES GP, WGP, APC and their respective affiliates) pursuant to the Merger Agreement, after giving effect to the pre-Merger transactions, was fair, from a financial point of view, to such holders.

The full text of Lazard’s written opinion, dated November 7, 2018, which sets forth the assumptions made, procedures followed, factors considered and qualifications and limitations on the review undertaken by Lazard in connection with its opinion, is attached as Annex B to this proxy statement/prospectus and is incorporated herein by reference. We encourage you to read Lazard’s opinion carefully and in its entirety.

Lazard’s opinion was provided for the use and benefit of the WES Special Committee (in its capacity as such) in its evaluation of the Transactions, and addressed only the fairness, as of the date of the opinion, from a financial point of view, to the holders of WES common units (other than WES GP, WGP, APC and their respective affiliates) of the Merger Consideration to be received by such holders of WES common units pursuant to the Merger Agreement, after giving effect to the pre-Merger transactions. Lazard’s opinion is not intended to and does not constitute a recommendation to any unitholder as to how such unitholder should vote or act with respect to the Merger or any matter relating thereto.

Lazard’s opinion was necessarily based on economic, monetary, market and other conditions as in effect on, and the information made available to Lazard as of, the date of Lazard’s opinion. Lazard assumed no responsibility for updating or revising its opinion based on circumstances or events occurring after the date of Lazard’s opinion. Lazard did not express any opinion as to the price at which WES common units or WGP common units may trade at any time subsequent to the announcement of the Transactions. Lazard was not authorized to, and did not, solicit indications of interest from third parties regarding a potential transaction with WES. Lazard’s opinion does not address the relative merits of the Transactions as compared to any other transaction or business strategy in which WES might engage or the merits of the underlying decision by WES to engage in the Transactions.

In connection with its opinion, Lazard:

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Lazard assumed and relied upon the accuracy and completeness of the foregoing information, without independent verification of such information. Lazard did not conduct any independent valuation or appraisal of any of the assets or liabilities (contingent or otherwise) of WES or WGP or of the Contributed Interests or the Purchased Interests or concerning the solvency or fair value of WES or WGP, and was not furnished with any such valuation or appraisal. With respect to the financial forecasts utilized in Lazard’s analyses, Lazard assumed, with the consent of the WES Special Committee, that such analyses were reasonably prepared on bases reflecting the best currently available estimates and judgments as to the future financial performance of WES and WGP, respectively. Lazard assumed no responsibility for and expressed no view as to any such forecasts or the assumptions on which they were based.

In rendering its opinion, Lazard assumed, with the consent of the WES Special Committee, that the Transactions would be consummated on the terms described in the Merger Agreement, without any waiver or modification of any material terms or conditions. Lazard assumed that the Merger Agreement, when executed, would conform to the draft reviewed by Lazard in all material respects. Lazard also assumed, with the consent of the WES Special Committee, that obtaining the necessary governmental, regulatory or third party approvals and consents for the Transactions would not have an adverse effect on WES, WGP, or the Transactions. Lazard did not express any opinion as to any tax or other consequences that might result from the Transactions, nor does Lazard’s opinion address any legal, tax, regulatory or accounting matters, as to which Lazard understands that the WES Special Committee obtained such advice as it deemed necessary from qualified professionals. Lazard expressed no view or opinion as to any terms or other aspects (other than the Merger Consideration to the extent expressly specified in Lazard’s opinion) of the Merger, including, without limitation, the form or structure of the Merger or any agreements or arrangements entered into in connection with, or contemplated by, the Merger. In addition, Lazard expressed no view or opinion as to the fairness of any of the pre-Merger transactions, individually or taken as a whole, or of the amount or nature of, or any other aspects relating to, the compensation to any officers, directors or employees of any parties to the Transactions, or class of such persons, relative to the Merger Consideration or otherwise.

The following is a summary of the material financial analyses reviewed with the WES Special Committee in connection with Lazard’s opinion, dated November 7, 2018. The summary of Lazard’s analyses provided below is not a complete description of the analyses underlying Lazard’s opinion. The preparation of a fairness opinion is a complex process involving various determinations as to the most appropriate and relevant methods of financial analysis and the application of those methods to particular circumstances and, therefore, is not readily susceptible to summary description.

In arriving at its opinion, Lazard considered the results of all of the analyses undertaken by it and assessed as a whole and did not draw, in isolation, conclusions from or with regard to any factor or method of analysis considered by it. Rather, Lazard made its determination as to fairness on the basis of its experience and professional judgment after considering the results of all of the analyses. Considering selected portions of the analyses in the summary set forth below, without considering the analyses as a whole, could create an incomplete or misleading view of the analyses underlying Lazard’s opinion.

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For purposes of its analyses and reviews, Lazard considered economic, monetary, market and other conditions, many of which are beyond the control of WES and WGP. No company, business or transaction used in Lazard’s analyses is identical to WES, WGP or the Transactions, and an evaluation of the results of those analyses is not entirely mathematical. Rather, the analyses involve complex considerations and judgments concerning financial and operating characteristics and other factors that could affect the public trading or other values of the companies, businesses or transactions used in Lazard’s analyses. The estimates contained in Lazard’s analyses and the ranges of valuations resulting from any particular analysis are not necessarily indicative of actual values or predictive of future results or values, which may be significantly more or less favorable than those suggested by Lazard’s analyses. In addition, analyses relating to the value of companies, businesses or securities do not purport to be appraisals or to reflect the prices at which companies, businesses or securities actually may be sold. Accordingly, the estimates used in, and the results derived from, Lazard’s analyses are inherently subject to substantial uncertainty.

The summary of the analyses provided below includes information presented in tabular format. In order to fully understand Lazard’s analyses, the tables must be read together with the full text of each summary. The tables alone do not constitute a complete description of Lazard’s analyses. Considering the data in the tables below without considering the full description of the analyses, including the methodologies and assumptions underlying the analyses, could create a misleading or incomplete view of Lazard’s analyses.

Except as otherwise noted, the following quantitative information, to the extent that it is based on market data, is based on market data as it existed on or before November 7, 2018 and is not necessarily indicative of current market conditions. As used in this section with respect to WES, WGP and APC, references to EBITDA mean Adjusted EBITDA as prepared by management of WES, WGP and APC and defined under “The Merger—Unaudited Financial Projections.”

Stand-alone Analyses of WES

In conducting stand-alone valuation analyses for WES, Lazard relied on financial projections (the “WES Projections”) of WES furnished to Lazard by WES’s management team. These projections included forecasted distributable cash flow (“DCF”) and distributions per unit projections from the second half of 2018 through the end of 2021.

Lazard performed a dividend discount model analysis of the WES common units, which calculates an implied equity value per unit by discounting to the present the value of the future distributions per WES common unit expected to be paid by WES in the period from the second half of 2018 through 2021.

Lazard based its dividend discount model analysis for WES on an assumed equity discount rate ranging from 9.0% to 11.0%. Lazard also calculated estimated terminal values for WES by applying terminal multiples ranging from 8.25x to 10.25x to WES’s estimated terminal DCF, which was projected using a growth rate derived from the WES Projections. Lazard chose these ranges for this analysis based on its analysis of the relevant metrics for the WES comparable companies (as set forth below), as well as its professional judgment and experience.

The resulting range of implied per unit equity values for WES common units was $42.50 to $52.50.

Lazard reviewed and analyzed certain financial information, valuation multiples and market trading data related to selected comparable publicly traded midstream gathering and processing companies whose operations Lazard believed, based on its experience with companies in the midstream gathering and processing industry and its professional judgment, to be generally relevant for the purposes of this analysis.

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In conducting the comparable company analysis with respect to WES, Lazard looked at multiple peer companies, including some that have (or recently had) upstream corporate sponsors and some that do not. The selected group of upstream-sponsored companies Lazard used in this analysis with respect to WES, referred to herein as the “E&P-Sponsored WES Comparable Companies,” was as follows:

The selected group of companies without upstream sponsors that Lazard used in this analysis with respect to WES, referred to herein as the “Other WES Comparable Companies,” was as follows:

The information reviewed and compared included:

The resulting high, low, mean and median data for the E&P-Sponsored WES Comparable Companies was:

The resulting high, low, mean and median data for the Other WES Comparable Companies was:

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This analysis resulted in an implied price per unit range for WES common units with reference to the analysis of both the E&P-Sponsored WES Comparable Companies and the Other WES Comparable Companies combined as set forth below:

The overall resulting range of implied per unit equity values for WES common units was $36.25 to $46.25.

Lazard reviewed the financial terms of certain transactions since May of 2015 by MLPs, public general partners (“GPs”) and corporations, including transactions where the target company is an MLP, that Lazard deemed similar to the Transactions in one or more respects. The information reviewed and compared included the percentage premium paid over the acquired company’s unit price one day prior to the announcement of the acquisition and the price per unit as a multiple of current and next year estimated DCF per unit, based on publicly available information and research analyst estimates for those targets.

The selected transactions and resulting current year P/DCF data were:

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The overall resulting range of implied per unit equity values for WES common units was $46.50 to $54.75.

Stand-alone Analyses of WGP

In conducting stand-alone valuation analyses for WGP, Lazard relied on financial projections (the “WGP Projections”) of WGP furnished to Lazard by WES’s management team. These projections included forecasted DCF and distributions per unit projections from the second half of 2018 through the end of 2021.

Lazard performed a dividend discount model analysis of the WGP common units, which calculates an implied equity value per unit by discounting to the present the value of the future distributions per WGP common unit expected to be paid by WGP in the period from the second half of 2018 through 2021.

Lazard based its dividend discount model analysis for WGP on an assumed equity discount rate ranging from 9.0% to 11.0%. Lazard also calculated estimated terminal values for WGP by applying terminal multiples ranging from 10.00x to 12.00x to WGP’s estimated terminal DCF, which was projected using a growth rate derived from the WGP Projections. Lazard chose these ranges for this analysis based on its analysis of the relevant metrics for the WGP Comparable Companies (as defined below), as well as its professional judgment and experience.

The resulting range of implied per unit equity values for WGP common units was $32.25 to $39.25.

Lazard reviewed and analyzed certain financial information, valuation multiples and market trading data related to selected comparable publicly traded GPs of midstream companies who Lazard believed, based on its experience with such entities and its professional judgment, to be generally relevant for the purposes of this analysis.

In conducting the comparable company analysis with respect to WGP, Lazard looked at multiple peer companies. The selected group of companies Lazard used in this analysis with respect to WGP, referred to herein as the “WGP Comparable Companies,” was as follows:

The information reviewed and compared included:

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The resulting high, low, mean and median data for the companies used in the comparable company analysis for WGP was:

This analysis resulted in an implied price per unit range for WGP common units as set forth below:

The overall resulting range of implied per unit equity values for WGP common units was $26.25 to $31.75.

Stand-alone Analysis of the Dropdown Assets

In conducting stand-alone valuation analyses for the Contributed Interests and the Purchased Interests (together, the “Dropdown Assets”), Lazard relied on financial projections (the “Dropdown Asset Projections”) of the Dropdown Assets furnished to Lazard by WES’s management team. These projections included the Dropdown Assets’ forecasted Adjusted EBITDA from the second half of 2018 through the end of 2021.

A discounted cash flow analysis is a valuation methodology used to derive a valuation of a company by calculating the present value of its estimated future cash flows. “Future cash flows” refers to projected unlevered free cash flows of a company. “Present” value refers to the current value of future cash flows or amounts and is obtained by discounting future cash flows or amounts by a discount rate that takes into account macroeconomic assumptions and estimates of risk, the opportunity cost of capital, capital structure, income taxes, expected returns and other appropriate factors. Lazard performed a discounted cash flow analysis with respect to the Dropdown Assets.

Lazard performed this analysis using weighted average cost of capital rates ranging from 7.5% to 10.0%. Lazard also calculated estimated terminal values for the Dropdown Assets by applying terminal multiples ranging from 8.50x to 10.25x to the terminal Adjusted EBITDA of the Dropdown Assets which was provided as part of the Dropdown Asset Projections. Lazard chose these ranges for this analysis based on its analysis of the relevant metrics for the Dropdown Comparable Companies (as defined below), as well as its professional judgment and experience.

The overall resulting range of total enterprise value for the Dropdown Assets based off this analysis was $4.70 billion to $5.54 billion.

Lazard reviewed and analyzed certain financial information, valuation multiples and market trading data related to selected comparable publicly traded midstream companies whose operations Lazard believed, based on its experience with companies in the midstream industry and its professional judgment, to be generally relevant for the purposes of the Dropdown Asset analysis.

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In conducting the comparable company analysis with respect to the Dropdown Assets, Lazard looked at multiple peer companies. To compare each component company of the Dropdown Assets to its most relevant peer company, Lazard conducted two separate comparable company analyses with the respect to the Dropdown Assets. One analysis reviewed and compared peer companies comprised primarily of gathering and processing assets (“G&P Assets”), and the other analysis reviewed and compared peer companies comprised primarily of pipeline joint venture assets (“Pipeline Joint Venture Assets”).

The selected group of G&P Asset companies Lazard used in this analysis with respect to the Dropdown Assets, referred to herein as the “G&P Asset Dropdown Comparable Companies,” was as follows:

The selected group of Pipeline Joint Venture Asset companies that Lazard used in this analysis with respect to the Dropdown Assets, referred to herein as the “Pipeline Joint Venture Asset Dropdown Comparable Companies,” was as follows:

The information reviewed and compared for each of the G&P Asset Dropdown Comparable Companies, and the Pipeline Joint Venture Asset Dropdown Comparable Companies (collectively, the “Dropdown Comparable Companies”) included:

The resulting high, low, mean and median data for the G&P Asset Dropdown Comparable Companies was:

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The resulting high, low, mean and median data for the Pipeline Joint Venture Asset Dropdown Comparable Companies was:

The overall resulting range of total enterprise value for the Dropdown Assets based off this analysis was $4.41 billion to $4.86 billion.

To perform the selected precedent transaction analysis with respect to the Dropdown Assets, Lazard reviewed selected publicly available information for 32 transactions between October 2014 and October 2018 involving G&P Asset companies (the “G&P Transactions”) that Lazard believed, based on its experience with transactions in the midstream gathering and processing industry and its professional judgment, to be generally relevant for the purposes of this analysis. Also, as part of this analysis, Lazard separately reviewed publicly available information for 27 other transactions occurring between May 2014 and August 2018 involving Pipeline Joint Venture Asset companies (the “Pipeline JV Transactions”) that Lazard believed, based on its experience with transactions in the midstream gathering and processing industry and its professional judgment, to be generally relevant for the purposes of this analysis.

The G&P Transactions (which involved the acquisition of all, or a portion of, the relevant interests of the target companies or assets listed in the “Target” column) and resulting mean, median and percentile data were:

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The Pipeline JV Transactions (which involved the acquisition of all, or a portion of, the relevant interests of the target companies or assets listed in the “Target” column) and resulting mean, median and percentile data were:

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