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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT
Pursuant to Section 13 or 15(d) of the
Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): November 16, 2015

MARKWEST ENERGY PARTNERS, L.P.

(Exact name of registrant as specified in its charter)

Delaware	001-31239	27-0005456
(State or other jurisdiction of incorporation or organization)	(Commission File Number)	(IRS Employer Identification No.)

1515 Arapahoe Street, Tower 1, Suite 1600, Denver CO 80202

(Address of principal executive officers)

Registrant’s telephone number, including area code: 303-925-9200

Not Applicable.

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

x     Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o      Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

oPre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

oPre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 1.01. Entry into a Material Definitive Agreement.

Amendment No. 2

On November 16, 2015, MarkWest Energy Partners, L.P., a Delaware limited partnership (the “Partnership”), MPLX LP, a Delaware limited partnership (“MPLX”), MPLX GP LLC, a Delaware limited liability company and the general partner of MPLX (“MPLX GP”), Sapphire Holdco LLC, a Delaware limited liability company and wholly owned subsidiary of MPLX (“Merger Sub”), and, for certain limited purposes set forth in the Amendment, Marathon Petroleum Corporation, a Delaware corporation and the parent of MPLX GP (“MPC”), entered into Amendment Number 2 (“Amendment Number 2”) to the Agreement and Plan of Merger dated as of July 11, 2015 (as previously amended, the “Merger Agreement” and, together with Amendment Number 2, the “Amended Merger Agreement”), among the Partnership, MPLX, MPLX GP, Merger Sub and, for certain limited purposes set forth in the Merger Agreement, MPC, pursuant to which Merger Sub will be merged with and into the Partnership (the “Merger”), with the Partnership surviving the Merger as a wholly owned subsidiary of MPLX.

Amendment Number 2 provides that the cash consideration to be received by the Partnership’s common unitholders, including all holders of Canceled Awards (as defined below), will be $6.20 per common unit.  MPC will contribute approximately $1,280 million in cash, representing all the cash necessary to pay the aggregate Cash Consideration (as defined below), to MPLX, without receiving any new equity in exchange.  As a result, under the Amended Merger Agreement, at the effective time of the Merger (the “Effective Time”), (a) each outstanding Partnership common unit (the “Common Units”), including all Canceled Awards, will be converted into the right to receive 1.09 MPLX common units (such consideration, the “Common Equity Consideration”) and $6.20 in cash per Common Unit (the “Cash Consideration” and, together with the Common Equity Consideration, the “Common Merger Consideration”) and (b) each outstanding Partnership class B unit will be converted into the right to receive 1 MPLX class B unit. Under the Amended Merger Agreement, at the Effective Time, the Partnership class A units, all of which are owned by wholly owned subsidiaries of the Partnership, will be converted into a specified number of MPLX class A units, as more fully described in the Amended Merger Agreement.

As a result of the Merger, each phantom unit of Common Units under the Partnership’s equity plans that is outstanding immediately prior to the Effective Time will become fully vested and converted into an equivalent number of Common Units, which will be canceled and converted into the right to receive the Common Merger Consideration (each Phantom Unit, as so converted, a “Canceled Award”).

Other than as previously modified by the Amendment to the Merger Agreement, dated November 10, 2015, among the Partnership, MPLX, MPLX GP , Merger Sub, and MPC, which was filed as Exhibit 2.1 to the Current Report on Form 8-K filed with the Securities and Exchange Commission (“SEC”) by the Partnership on November 10, 2015, and except as expressly modified pursuant to Amendment Number 2, the Merger Agreement, which was filed as Exhibit 2.1 to the Current Report on Form 8-K filed with the SEC by the Partnership on July 13, 2015, remains in full force and effect as originally executed on July 11, 2015. The foregoing description of Amendment Number 2 and the transactions contemplated thereby does not purport to be complete and is subject to, and qualified in its entirety by, the full text of Amendment Number 2, which is attached hereto as Exhibit 2.1 to this Current Report on Form 8-K and is incorporated by reference in this Item 1.01.

Voting Agreements

On November 16, 2015, in connection with the execution of Amendment No. 2, each of Kayne Anderson Capital Advisors, L.P., which as of the close of business on October 5, 2015, the record date for the Partnership’s special meeting of common unitholders to be held on December 1, 2015, had voting power over approximately 11,137,719 Common Units (representing approximately 5.7% of the Common Units entitled to vote at the Partnership’s special meeting), and Tortoise Capital Advisors, L.L.C., which as of the close of business on October 5, 2015 had voting power over 11,499,731 Common Units (representing approximately 5.9% of the Common Units entitled to vote at Partnership’s the special meeting), entered into Voting Agreements with MPLX, MPLX GP and Merger Sub, pursuant to which each has agreed, among other things, to vote (or cause to be voted) all Common Units owned by them in favor of approving the Amended Merger Agreement.  Each of the Voting Agreements shall terminate upon termination of the Amended Merger Agreement and certain other specified events.

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The foregoing description of the Voting Agreements does not purport to be complete and is subject to, and qualified in its entirety by, the full text of the Voting Agreements, which are attached hereto as Exhibit 99.2 and Exhibit 99.3 to this Current Report on Form 8-K and are incorporated by reference in this Item 1.01.

Item 8.01. Other Events.

On November 17, 2015, the Partnership issued a joint press release with MPLX announcing the execution of Amendment Number 2.  A copy of the press release issued is filed as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated by reference in this Item 8.01.

Item 9.01. Financial Statements and Exhibits.

(d)           Exhibits

Exhibit No.	Description
2.1	Amendment Number 2 to Agreement and Plan of Merger, dated as of November 16, 2015, by and among MarkWest Energy Partners, L.P., MPLX LP, MPLX GP LLC, Marathon Petroleum Corporation and Sapphire Holdco LLC
99.1	Press Release dated November 17, 2015, issued by MarkWest Energy Partners, L.P. and MPLX LP
99.2	Voting Agreement, dated as of November 16, 2015, by and among MPLX LP, MPLX GP LLC, Sapphire Holdco LLC, Kayne Anderson Capital Advisors, L.P. and KA Fund Advisors, LLC
99.3	Voting Agreement, dated as of November 16, 2015, by and among MPLX LP, MPLX GP LLC, Sapphire Holdco LLC and Tortoise Capital Advisors, L.L.C.

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Cautionary Statement Regarding Forward-Looking Statements

This communication includes “forward-looking statements.” All statements other than statements of historical facts included or incorporated herein may constitute forward-looking statements that involve a number of risks and uncertainties. These statements may include statements regarding the proposed acquisition of the Partnership by MPLX, the expected timetable for completing the transaction, benefits and synergies of the transaction, future opportunities for the combined company and any other statements regarding the Partnership’s and MPLX’s future operations, anticipated business levels, future earnings and distributions, planned activities, anticipated growth, market opportunities, strategies and competition. All such forward-looking statements involve estimates and assumptions that are subject to a number of risks, uncertainties and other factors that could cause actual results to differ materially from those expressed or implied in such statements. Factors that could cause or contribute to such differences include: factors relating to the satisfaction of the conditions to the proposed transaction, including regulatory approvals and the required approval of the Partnership’s unitholders; the parties’ ability to meet expectations regarding the timing and tax treatment of the proposed transaction; the possibility that the combined company may be unable to achieve expected synergies and operating efficiencies in connection with the transaction within the expected time-frames or at all; the integration of the Partnership being more difficult, time-consuming or costly than expected; the effect of any changes resulting from the proposed transaction in customer, supplier and other business relationships; general market perception of the proposed transaction; exposure to lawsuits and contingencies associated with MPLX; the ability to attract and retain key personnel; prevailing market conditions; changes in the economic and financial conditions of the Partnership and MPLX; uncertainties and matters beyond the control of management; and the other risks discussed in the periodic reports filed with the SEC, including the Partnership’s and MPLX’s Annual Reports on Form 10-K for the year ended December 31, 2014 and the Partnership’s and MPLX’s subsequent reports on Form 10-Q. These risks, as well as other risks associated

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with the Partnership, MPLX and the proposed transaction, are also more fully discussed in the definitive proxy statement/prospectus referred to below.  The forward-looking statements should be considered in light of all these factors. In addition, other risks and uncertainties not presently known to the Partnership or MPLX or that the Partnership or MPLX considers immaterial could affect the accuracy of the forward-looking statements. The reader is cautioned not to rely unduly on these forward-looking statements. The Partnership and MPLX do not undertake any duty to update any forward-looking statement except as required by law.

Additional Information and Where to Find It

This communication may be deemed to be solicitation material in respect of the proposed acquisition of the Partnership by MPLX. In connection with the proposed acquisition, the Partnership and MPLX have filed relevant materials with the SEC, including MPLX’s registration statement on Form S-4 which included a definitive proxy statement/prospectus and was declared effective by the SEC on October 29, 2015, and the Partnership’s definitive proxy statement/proxy statement which was filed with the SEC on October 30, 2015 and mailed to the Partnership’s common unitholders on or about October 30, 2015.  Investors and security holders are urged to read all relevant documents filed with the SEC, including the definitive proxy statement/prospectus, because they contain important information about the proposed transaction. Investors and security holders are able to obtain the documents free of charge at the SEC’s website, http://www.sec.gov, or for free from the Partnership by contacting Investor Relations by phone at 1-(866) 858-0482 or by email at investorrelations@markwest.com or for free from MPLX LP at its website, http://ir.mplx.com, or in writing at 200 E. Hardin Street, Findlay, Ohio 45840, Attention: Corporate Secretary.

Participants in the Solicitation

This communication is not a solicitation of a proxy from any investor or securityholder. However, the Partnership and its directors and executive officers and certain employees may be deemed to be participants in the solicitation of proxies from the holders of Partnership common units with respect to the proposed transaction. Information about the Partnership’s directors and executive officers is set forth in the proxy statement for the Partnership’s 2015 Annual Meeting of Common Unitholders, which was filed with the SEC on April 23, 2015 and the Partnership’s current reports on Form 8-K, as filed with the SEC on May 5, 2015, May 19, 2015 and June 8, 2015. Information about MPLX’s directors and executive officers is available in MPLX’s Annual Report on Form 10-K filed with the SEC on February 27, 2015 and MPLX’s current report on Form 8-K, as filed with the SEC on March 9, 2015. To the extent holdings of Partnership securities have changed since the amounts contained in the proxy statement for the Partnership’s 2015 Annual Meeting of stockholders, such changes have been or will be reflected on Statements of Change in Ownership on Form 4 filed with the SEC. Additional information regarding those persons and other persons who may be deemed to be participants in the solicitation of proxies from the holders of Partnership common units with respect to the proposed transaction, including their respective direct and indirect interests in the proposed transaction, by security holdings or otherwise, is contained in the definitive proxy statement/prospectus and other relevant materials filed with the SEC referred to above. These documents may be obtained free of charge from the SEC’s website http://www.sec.gov, or from the Partnership and MPLX, as applicable, using the contact information above.

Non-Solicitation

This communication shall not constitute an offer to sell or the solicitation of an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offer of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended.

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SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this Report to be signed on its behalf by the undersigned hereunto duly authorized.

	MarkWest Energy Partners, L.P.
	By: MarkWest Energy GP, L.L.C., its general partner
Date: November 17, 2015	By:	/s/ Nancy K. Buese
		Name:	Nancy K. Buese
		Title:	Executive Vice President and Chief Financial Officer

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EXHIBIT INDEX

Exhibit No.	Description
2.1	Amendment to Agreement and Plan of Merger, dated as of November 16, 2015, by and among MarkWest Energy Partners, L.P., MPLX LP, MPLX GP LLC, Marathon Petroleum Corporation and Sapphire Holdco LLC
99.1	Press Release dated November 17, 2015, issued by MarkWest Energy Partners, L.P. and MPLX LP
99.2	Voting Agreement, dated as of November 16, 2015, by and among MPLX LP, MPLX GP LLC, Sapphire Holdco LLC, Kayne Anderson Capital Advisors, L.P. and KA Fund Advisors, LLC
99.3	Voting Agreement, dated as of November 16, 2015, by and among MPLX LP, MPLX GP LLC, Sapphire Holdco LLC and Tortoise Capital Advisors, L.L.C.

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EX-2.1

Exhibit 2.1

EXECUTION VERSION

AMENDMENT NUMBER 2 TO AGREEMENT AND PLAN OF MERGER

THIS AMENDMENT NUMBER 2 TO AGREEMENT AND PLAN OF MERGER, dated as of November 16, 2015 (this “Amendment”), is made by and among MarkWest Energy Partners, L.P., a Delaware limited partnership (the “Partnership”), MPLX LP, a Delaware limited partnership (“Parent”), MPLX GP LLC, a Delaware limited liability company and the general partner of Parent (“Parent GP”), solely for purposes of Section 5.15 of the Merger Agreement (defined below), Marathon Petroleum Corporation, a Delaware corporation and the ultimate parent of Parent GP (“MPC”), and Sapphire Holdco LLC, a Delaware limited liability company and a wholly owned Subsidiary of Parent (“Merger Sub” and, with MPC, Parent and Parent GP, the “Parent Entities”).

RECITALS

1.The Parent Entities and the Partnership are parties to that certain Agreement and Plan of Merger, dated as of July 11, 2015 (as amended, the “Merger Agreement”).

2.The Parent Entities and the Partnership are parties to that certain Amendment to Agreement and Plan of Merger, dated as of November 10, 2015.

3.Pursuant to Section 8.2 of the Merger Agreement, the Parent Entities and the Partnership desire to further amend the Merger Agreement as set forth herein.

4.Item 3 of Section 5.2(a)(i) of the Partnership Disclosure Schedule permitted the Partnership to issue equity and incur indebtedness subject to a 4.5x leverage ratio; provided that such equity issuance was not to exceed $1.0 billion in the aggregate.

5.All capitalized terms used, but not defined, in this Amendment shall have the meanings ascribed thereto in the Merger Agreement.

6.In consideration of the foregoing, the representations, warranties, covenants and agreements set forth in this Amendment and the Merger Agreement, and other good and valuable consideration, the adequacy and receipt of which are hereby acknowledged, the parties, intending to be legally bound, hereby agree as follows:

SECTION 1.  Amendments To The Merger Agreement.  The parties hereby agree to amend the Merger Agreement and the Partnership Disclosure Letter as follows:

(a)Section 2.1(a) of the Merger Agreement is hereby amended and restated in its entirety to read as follows:

“Subject to Section 2.1(d), Section 2.2(h) and Section 2.3, (i) each Common Unit (including all Canceled Awards) issued and outstanding as of immediately

prior to the Effective Time will be converted into the right to receive 1.09 (the “Common Unit Equity Consideration” and such ratio the “Exchange Ratio”) Parent Units and cash in an amount of $6.20 per Common Unit (including all Canceled Awards) (the “Cash Consideration”, and together with the Common Unit Equity Consideration, the “Common Merger Consideration”), (ii) each Class A Unit issued and outstanding as of immediately prior to the Effective Time will be converted into the right to receive (x) 1.09 Parent Class A Units plus (y) the number of Parent Class A Units equal to a fraction, the numerator of which is the Fully Diluted Cash Consideration and the denominator of which is the closing trading price of Parent Units on the trading day immediately preceding the Closing Date (the “Class A Consideration” and such ratio the “Class A Exchange Ratio”)  and (iii) each Class B Unit issued and outstanding as of immediately prior to the Effective Time will be converted into the right to receive 1 Parent Class B Unit (the “Class B Consideration” and such ratio, the “Class B Exchange Ratio”).  As used in this Agreement, “Fully Diluted Cash Consideration” means a fraction, the numerator of which is the aggregate dollar amount obtained by multiplying the Cash Consideration by the sum of (x) the number of Common Units (including all Canceled Awards) plus (y) the number of Class B Units, in each case outstanding immediately prior to the Effective Time, and the denominator of which is the number of Common Units (including all Canceled Awards) plus the number of Class A Units plus the number of Class B Units, in each case outstanding immediately prior to the Effective Time.”

(b)Item 3 of Section 5.2(a)(i) of the Partnership Disclosure Schedule is hereby amended by adding the following proviso at the end thereof:

“; provided further that, notwithstanding the foregoing, the Partnership shall not issue equity pursuant to this Item 3 of this Section 5.2(a)(i) from and after November 13, 2015 without the prior consent of Parent (which consent will not be unreasonably withheld, delayed or conditioned).”

SECTION 2.  Effectiveness of Amendment.  Upon the execution and delivery of this Amendment, the Merger Agreement will thereupon be deemed to be amended as hereinabove set forth as fully and with the same effect as if the amendments made hereby were originally set forth in the Merger Agreement, and this Amendment and the Merger Agreement will henceforth respectively be read, taken and construed as one and the same instrument.

SECTION 3. Reaffirmation by the Parent Entities.  Parent hereby makes and reaffirms the representations and warranties contained in Section 4.2(e) and Section 4.17 of the Merger Agreement, and MPC hereby reaffirms the covenants set forth in Section 5.15(b) of the Merger Agreement, after giving effect to the amendments effected pursuant to Section 1 hereof.

SECTION 4. Partnership Authority Relative to Amendment.  The Partnership has all requisite power and authority to execute and deliver this Amendment and to

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consummate the transactions contemplated hereby, subject to obtaining the Partnership Unitholder Approval.  The execution, delivery and performance by the Partnership of this Amendment, and the transactions contemplated hereby, have been duly authorized and approved by the General Partner, which, at a meeting duly called and held, has (i) approved and declared advisable this Amendment and the transactions contemplated hereby and (ii) resolved to submit the Merger Agreement, as amended by this Amendment, to a vote of the Limited Partners of the Partnership and to recommend approval of the Merger Agreement, as amended by this Amendment, by the Limited Partners of the Partnership, and except for obtaining the Partnership Unitholder Approval for the approval of the Merger Agreement, as amended by this Amendment, and consummation of the transactions contemplated hereby, no other partnership action on the part of the Partnership is necessary to authorize the execution, delivery and performance by the Partnership of this Amendment and the consummation of the transactions contemplated hereby.  This Amendment has been duly executed and delivered by the Partnership and, assuming due authorization, execution and delivery, of this Amendment by the other parties hereto, constitutes a legal, valid and binding obligation of the Partnership, enforceable against it in accordance with its terms.

SECTION 5. Parent Entities Authority Relative to Amendment.  Each of the Parent Entities has all requisite power and authority to execute and deliver this Amendment and to consummate the transactions contemplated hereby.  The execution, delivery and performance by the Parent Entities of this Amendment, and the consummation of the transactions contemplated hereby, have been duly authorized and approved by Merger Sub and Parent, as its sole member, by Parent GP, for itself and on behalf of Parent, and by MPC and no other entity action on the part of the Parent Entities is necessary to authorize the execution, delivery and performance by the Parent Entities of this Amendment and the consummation of the transactions contemplated hereby.  This Amendment has been duly executed and delivered by the Parent Entities and, assuming due authorization, execution and delivery of this Amendment by the Partnership, constitutes a legal, valid and binding obligation of each of the Parent Entities, enforceable against each of them in accordance with its terms.

SECTION 6. References to the Merger Agreement.  After giving effect to this Amendment, each reference in the Merger Agreement to “this Agreement”, “hereof”, “hereunder”, “herein” or words of like import referring to the Merger Agreement shall refer to the Merger Agreement as amended by this Amendment, and all references in the Parent Disclosure Letter and the Partnership Disclosure Letter to “the Agreement” shall refer to the Merger Agreement as amended by this Amendment.

SECTION 7. Construction.  Except as expressly provided in this Amendment, all references in the Merger Agreement, the Parent Disclosure Letter and the Partnership Disclosure Letter to “the date hereof” and “the date of this Agreement” or words of like import shall refer to July 11, 2015.

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SECTION 8.  General Provisions.

(a)Miscellaneous.  Sections 8.1 through 8.10 and Section 8.12 of the Merger Agreement are incorporated by reference into this Amendment and will apply to the Parent Entities and the Partnership mutatis mutandis.

(b)Agreement in Effect.  Except as specifically provided for in this Amendment, the Merger Agreement will remain unmodified and in full force and effect.

[Signature Pages Follow]

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IN WITNESS WHEREOF, the parties have caused this Amendment to be duly executed and delivered as of the date first above written.

PARENT:
MPLX LP
By:	MPLX GP LLC,
	its general partner
By:	/s/ G.R. Heminger
Name: G.R. Heminger
Title: Chairman and Chief Executive Officer
PARENT GP:
MPLX GP LLC
By:	/s/ G.R. Heminger
Name: G.R. Heminger
Title: Chairman and Chief Executive Officer
MERGER SUB:
SAPPHIRE HOLDCO LLC
By:	/s/ P.K.M. Beall
Name: P.K.M. Beall
Title: President
MPC:
MARATHON PETROLEUM CORPORATION
By:	/s/ G.R. Heminger
Name: G.R. Heminger
Title: President and Chief Executive Officer

[Signature Page to Amendment Number 2 to Merger Agreement]

PARTNERSHIP:
MARKWEST ENERGY PARTNERS, L.P.,
By:	MARKWEST ENERGY GP, L.L.C.,
	its general partner
By:	/s/ Frank M. Semple
Name:	Frank M. Semple
Title:	Chairman, President and Chief Executive Officer

[Signature Page to Amendment Number 2 to Merger Agreement]

EX-99.1

Exhibit 99.1

MPLX/MarkWest Combination Receives Further Cash Consideration
from Marathon Petroleum Corp.

·Marathon Petroleum Corporation increases one-time cash payment to $6.20 per unit on a best and final basis

·Total cash consideration of approximately $1.28 billion provides substantially enhanced value to MarkWest unitholders

·Three of MarkWest’s top unitholders, representing more than 15 percent of voting units, have agreed to vote in favor of the transaction

·MarkWest’s board and executive management affirm their support for the transaction and its revised terms

·Proxy supplement and proxy cards being mailed to unitholders

·Special unitholder meeting remains scheduled for Dec. 1, 2015

FINDLAY, Ohio, and DENVER, Nov. 17, 2015 — MPLX LP (NYSE: MPLX) and MarkWest Energy Partners, L.P. (NYSE: MWE) (MarkWest) today announced that, in connection with the anticipated combination of MPLX and MarkWest, Marathon Petroleum Corporation (NYSE:MPC) has agreed to further increase the amount of the one-time cash consideration payable to MarkWest common unitholders to $6.20 per unit, up from the cash consideration previously announced on Nov. 10, 2015, of approximately $5.21 per unit. This cash consideration represents a significant enhancement to the initial July 13, 2015, offer which was approximately $3.37 per unit. Under the revised terms of the merger agreement announced today, which represents the best and final offer, MarkWest common unitholders will receive approximately $1.28 billion in total cash consideration and 1.09 MPLX common units per MarkWest common unit, for a total consideration of approximately $51.74 per MarkWest common unit, based on the closing price of MPLX’s common units on Nov. 16, 2015.

Three of MarkWest’s largest unitholders, Kayne Anderson Capital Advisors, L.P., Tortoise Capital Advisors, L.L.C., and, as previously announced, The Energy & Minerals Group, which cumulatively represent more than 15 percent of MarkWest’s outstanding units entitled to vote, have all entered into voting agreements to vote in favor of the transaction. The merger is also recommended by each of the boards of directors of MPC, MPLX and MarkWest, and the executive management of both partnerships strongly support the transaction and its revised terms.

“We are pleased that three of MarkWest’s top unitholders have agreed to support the combination and vote in favor of this revised offer,” said Gary R. Heminger, MPLX chairman and chief executive officer.  “We look forward to consummating this transaction and delivering on the significant opportunities of the combined partnership.”

“This transaction will create long-term strategic value for our unitholders and customers through a combination of enhanced growth opportunities and significant parental support from Marathon Petroleum Corporation. This increased cash consideration from MPC further enhances the overall value of the transaction and our board and executive team recommend that MarkWest unitholders vote in favor of the merger proposal,” said Frank M. Semple, MarkWest chairman, president and chief executive officer.

The proposed transaction will combine MarkWest, the second-largest processor of natural gas in the United States and largest processor and fractionator in the Marcellus and Utica shale plays, with MPLX, a rapidly growing crude oil and refined products logistics partnership sponsored by MPC. The combination will create one of the largest master limited partnerships (MLPs), which is expected to generate a mid-20 percent compound annual distribution growth rate through 2019.

The transaction is subject to approval by MarkWest unitholders and other customary closing conditions and, subject to the satisfaction of those conditions, is expected to close in December 2015. The date of the special meeting of MarkWest common unitholders is Dec. 1, 2015. MarkWest unitholders of record as of Oct. 5, 2015, will be entitled to vote on approval of the merger and the associated proposals.

MarkWest unitholders are urged to vote “FOR” the merger and related matters and submit their proxy as promptly as possible, either by telephone, via the internet or by marking, signing and dating the proxy card that was provided to unitholders along with the proxy statement and prospectus. If you abstain from voting, fail to cast your vote in person or by proxy or fail to give voting instructions to your broker, bank or other nominee, it will have the same effect as a vote “AGAINST” the merger proposal.

MarkWest is mailing supplemental proxy materials to its unitholders.

Your vote is very important regardless of the number of MarkWest common units you own. The merger cannot be completed unless the holders of at least a majority of the outstanding MarkWest common units, voting together as a single class, vote for the proposal to approve the merger agreement and the transactions contemplated thereby at the special meeting of MarkWest common unitholders (the “Merger Proposal”). At the special meeting, MarkWest common unitholders will also vote on an advisory compensation proposal (the “Advisory Compensation Proposal”) and on a proposal to adjourn the special meeting, if necessary, to solicit additional proxies if there are not sufficient votes to approve the merger agreement and transactions contemplated thereby at the time of the special meeting (the “Adjournment Proposal”).

If you have already voted and would like to revoke your proxy or change your vote, you may do so at any time before the special meeting of MarkWest common unitholders.  If you are a MarkWest common unitholder of record, you may revoke your proxy and/or change your vote, or if you have not yet voted you may do so, at any time before 11:59 p.m. Eastern Time on Nov. 30, 2015 (the “Telephone/Internet Deadline”) or before the polls close at the MarkWest special meeting by (1) sending a written notice, which is received prior to the Telephone/Internet Deadline, to MarkWest at 1515 Arapahoe Street, Tower 1, Suite 1600, Denver, Colorado 80202, Attn: Corporate Secretary, that bears a date later than the date of the proxy and states that you revoke your proxy, (2) submitting a valid, later-date proxy by mail, telephone or Internet that is received prior to the Telephone/Internet Deadline or (3) attending the special meeting of MarkWest common unitholders and voting by ballot in person (your attendance at the MarkWest special meeting will not, by itself, revoke any proxy that you have previously given).  If you hold your MarkWest common units in “street name,” you should follow the instructions of your broker, bank or other nominee regarding the revocation of proxies. If your broker allows you to submit a proxy via the Internet or by telephone, you may be able to change your vote by submitting a new proxy via the Internet or by telephone or by mail.

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About MPLX LP

MPLX is a fee-based, growth-oriented master limited partnership formed in 2012 by Marathon Petroleum Corporation to own, operate, develop and acquire pipelines and other midstream assets related to the transportation and storage of crude oil, refined products and other hydrocarbon-based products. Headquartered in Findlay, Ohio, MPLX’s assets consist of a 99.5 percent equity interest in a network of common carrier crude oil and products pipeline assets located in the Midwest and Gulf Coast regions of the United States and a 100 percent interest in a butane storage cavern located in West Virginia with approximately 1 million barrels of natural gas liquids storage capacity.

About MarkWest Energy Partners

MarkWest Energy Partners, L.P. is a master limited partnership that owns and operates midstream service businesses. MarkWest has a leading presence in many natural gas resource plays including the Marcellus Shale, Utica Shale, Huron/Berea Shale, Haynesville Shale, Woodford Shale and Granite Wash formation.

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MPLX Investor Relations Contacts:
Geri Ewing (419) 421-2071

Teresa Homan (419) 421-2965

MPLX Media Contacts:
Chuck Rice (419) 421-2521

Jamal Kheiry (419) 421-3312

MarkWest Investor Relations and Media Contact:
Joshua Hallenbeck (866) 858-0482

This press release contains forward-looking statements within the meaning of federal securities laws regarding MPLX LP (“MPLX”), Marathon Petroleum Corporation (“MPC”), and MarkWest Energy Partners, L.P. (“MWE”). These forward-looking statements relate to, among other things, expectations, estimates and projections concerning the business and operations of MPLX, MPC, and MWE. You can identify forward-looking statements by words such as “anticipate,” “believe,” “estimate,” “objective,” “expect,” “forecast,” “guidance,” “imply,” “plan,” “project,” “potential,” “could,” “may,” “should,” “would,” “will” or other similar expressions that convey the uncertainty of future events or outcomes. Such forward-looking statements are not guarantees of future performance and are subject to risks, uncertainties and other factors, some of which are beyond the companies’ control and are difficult to predict. In addition to other factors described herein that could cause MPLX’s or MWE’s actual results to differ materially from those implied in these forward-looking statements, negative capital market conditions, including a persistence or increase of the current yield on common units, which is higher than historical yields, could adversely affect MPLX’s ability to meet its distribution growth guidance, particularly with respect to the later years of such guidance. Factors that could cause MPLX’s or MWE’s actual results to differ materially from those implied in the forward-looking statements include: the ability to complete the proposed merger of MPLX and MWE on anticipated terms and timetable; the ability to obtain approval of the transaction by the unitholders of MWE and satisfy other conditions to the closing of the transaction contemplated by the merger agreement; risk that the synergies from the MPLX/MWE transaction may not be fully realized or may take longer to realize than expected; disruption from the MPLX/MWE transaction making it more difficult to maintain relationships with customers, employees or suppliers; risks relating to any unforeseen liabilities of MWE or MPLX, as applicable; the adequacy of MPLX’s and MWE’s respective capital resources and liquidity, including, but not limited to, availability of sufficient cash flow to pay distributions, and the ability to successfully execute their business plans and implement their growth strategies; the timing and extent of changes in commodity prices and demand for crude oil, refined products, feedstocks or other hydrocarbon-based products; volatility in and/or degradation of market and industry conditions; completion of pipeline capacity by competitors; disruptions due to equipment interruption or failure, including electrical shortages and power grid failures; the suspension, reduction or termination of MPC’s obligations under MPLX’s commercial agreements; each company’s ability to successfully implement its growth plan, whether through organic growth or acquisitions; modifications to earnings and distribution growth objectives; federal and state environmental, economic, health and safety, energy and other policies and regulations; changes to MPLX’s capital budget; other risk factors inherent to MPLX or MWE’s industry; and the factors set forth under the heading “Risk Factors” in MPLX’s Annual Report on Form 10-K for the year ended Dec. 31, 2014, filed with the Securities and Exchange Commission (SEC); and the factors set forth under the heading “Risk Factors” in MWE’s Annual Report on Form 10-K for the year ended Dec. 31, 2014, and Quarterly Report on Form 10-Q for the quarter ended September 30, 2015, filed with the SEC. These risks, as well as other risks associated with MPLX, MWE and the proposed transaction, are also more fully discussed in the joint proxy statement and prospectus included in the registration statement on Form S-4 filed by MPLX and declared effective by the SEC on October 29, 2015, as supplemented. Factors that could cause MPC’s actual results to differ materially from those implied in the forward-looking statements include: risks described above relating to the MPLX/MWE proposed merger; changes to the expected construction costs and timing of pipeline projects; volatility in and/or degradation of market and industry conditions; the availability and pricing of crude oil and other feedstocks; slower growth in domestic and Canadian crude supply; an easing or lifting of the U.S. crude oil export ban; completion of pipeline capacity to areas outside the U.S. Midwest; consumer demand for refined products; transportation

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logistics; the reliability of processing units and other equipment; MPC’s ability to successfully implement growth opportunities; modifications to MPLX earnings and distribution growth objectives; federal and state environmental, economic, health and safety, energy and other policies and regulations; other risk factors inherent to MPC’s industry; and the factors set forth under the heading “Risk Factors” in MPC’s Annual Report on Form 10-K for the year ended Dec. 31, 2014, filed with SEC. In addition, the forward-looking statements included herein could be affected by general domestic and international economic and political conditions. Unpredictable or unknown factors not discussed here, in MPLX’s Form 10-K, in MPC’s Form 10-K, or in MWE’s Form 10-K and Form 10-Qs could also have material adverse effects on forward-looking statements. Copies of MPLX’s Form 10-K are available on the SEC website, MPLX’s website at http://ir.mplx.com or by contacting MPLX’s Investor Relations office. Copies of MPC’s Form 10-K are available on the SEC website, MPC’s website at http://ir.marathonpetroleum.com or by contacting MPC’s Investor Relations office. Copies of MWE’s Form 10-K and Form 10-Qs are available on the SEC website, MWE’s website at http://investor.markwest.com or by contacting MWE’s Investor Relations office.

Additional Information and Where to Find It

In connection with the proposed acquisition, MWE and MPLX have filed relevant materials with the SEC, including MPLX’s registration statement on Form S-4 that includes a definitive joint proxy statement and a prospectus declared effective by the SEC on October 29, 2015 and a supplement to the proxy statement/prospectus to be filed on or about November 17, 2015. Investors and security holders are urged to read all relevant documents filed with the SEC, including the definitive joint proxy statement and prospectus, because they contain important information about the proposed transaction. Investors and security holders are able to obtain the documents free of charge at the SEC’s website, http://www.sec.gov, or for free from MPLX LP at its website, http://ir.mplx.com, or in writing at 200 E. Hardin Street, Findlay, Ohio 45840, Attention: Corporate Secretary, or for free from MWE by contacting Investor Relations by phone at 1-(866) 858-0482 or by email at investorrelations@markwest.com.

Participants in the Solicitation

MPLX and MWE and their respective directors and executive officers and certain employees may be deemed to be participants in the solicitation of proxies from the holders of MWE common units with respect to the proposed transaction. Information about MPLX’s directors and executive officers is available in MPLX’s Annual Report on Form 10-K filed with the SEC on February 27, 2015 and MPLX’s current report on Form 8-K, as filed with the SEC on March 9, 2015. Information about MWE’s directors and executive officers is set forth in the proxy statement for MWE’s 2015 Annual Meeting of Common Unitholders, which was filed with the SEC on April 23, 2015 and MWE’s current reports on Form 8-K, as filed with the SEC on May 5, 2015, May 19, 2015 and June 8, 2015, and in the definitive joint proxy statement filed by MPLX, which was declared effective by the SEC on October 29, 2015, and the supplement to the proxy statement/prospectus to be filed on or about November 17, 2015. To the extent holdings of MWE securities have changed since the amounts contained in the definitive joint proxy statement filed by MPLX, which was declared effective by the SEC on October 29, 2015, and the supplement to the proxy statement/prospectus to be filed on or about November 17, 2015, such changes have been or will be reflected on Statements of Change in Ownership on Form 4 filed with the SEC. Investors may obtain additional information regarding the interest of such participants by reading the definitive joint proxy statement and prospectus regarding the acquisition. These documents may be obtained free of charge from the SEC’s website http://www.sec.gov, or from MWE and MPLX using the contact information above.

Non-Solicitation

This communication shall not constitute an offer to sell or the solicitation of an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offer of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended.

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EX-99.2

Exhibit 99.2

VOTING AGREEMENT

This VOTING AGREEMENT (this “Agreement”), dated as of November 16, 2015, is entered into by and among MPLX LP, a Delaware limited partnership (“Parent”), MPLX GP LLC, a Delaware limited liability company and the general partner of Parent (“Parent GP”), and Sapphire Holdco LLC, a Delaware limited liability company and a wholly owned subsidiary of Parent (“Merger Sub” and, with Parent and Parent GP, the “Parent Entities”), and each of the Persons set forth on Schedule A hereto (each, a “Unitholder”), as investment adviser, manager or general partner on behalf of various record and beneficial owners. All terms used but not otherwise defined in this Agreement shall have the respective meanings ascribed to such terms in the Merger Agreement (as defined below).

WHEREAS, as of the date hereof, each Unitholder is the discretionary investment adviser, manager or general partner with respect to various record and beneficial owners (as defined in Rule 13d-3 under the Exchange Act) that own the aggregate number of Common Units set forth opposite such Unitholder’s name on Schedule A (all such units set forth on Schedule A next to the Unitholder’s name specify those units held as of October 5, 2015 (and not sold before the date of this Agreement), which is the record date for holders of Common Units entitled to vote on the transactions contemplated by the Merger Agreement and is referred to as the “Record Date”) (all such units being referred to herein as the “Subject Units”); and

WHEREAS,  the Parent Entities, Marathon Petroleum Corporation, a Delaware corporation and the ultimate parent of Parent GP (“MPC”), and MarkWest Energy Partners, L.P., a Delaware limited partnership (the “Partnership”), have entered into an Agreement and Plan of Merger, dated July 11, 2015, as amended on November 10, 2015 (as it may be further amended pursuant to the terms thereof, including pursuant to the Amendment (as defined below), the “Merger Agreement”), which provides, among other things, for the merger of Merger Sub with and into the Partnership, upon the terms and subject to the conditions set forth therein (the “Merger”) in accordance with the DRULPA, whereby each issued and outstanding Common Unit will be converted into the right to receive the consideration set forth in the Merger Agreement;

WHEREAS, concurrently with the execution and delivery hereof, the Parent Entities, MPC and the Partnership are entering into Amendment No. 2 to the Agreement and Plan of Merger (the “Amendment”), providing for an Exchange Ratio of 1.09 Parent Units and cash in an amount of $6.20 per Common Unit (the “Specified Consideration”);

NOW, THEREFORE, in consideration of the foregoing and the respective representations, warranties, covenants and agreements set forth below and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto, intending to be legally bound, do hereby agree as follows:

ARTICLE I
AGREEMENT TO VOTE

1.1          Agreement to Vote. Subject to the terms of this Agreement, and so long as the Unitholders remain entitled to receive not less than the Specified Consideration, each Unitholder

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hereby irrevocably and unconditionally agrees that, until the Termination Date with respect to such Unitholder, at any annual or special meeting of the unitholders of the Partnership, however called, including any adjournment or postponement thereof, and in connection with any action proposed to be taken by written consent of the unitholders of the Partnership, such Unitholder shall, in each case to the fullest extent that such Unitholder’s Subject Units are entitled to vote thereon, and unless otherwise directed in writing by Parent: (a) appear at each such meeting or otherwise cause all such Subject Units to be counted as present thereat for purposes of determining a quorum; and (b) vote (or cause to be voted), or deliver (or cause to be delivered) a written consent with respect to, all of its Subject Units (i) in favor of the (A) approval of the Merger Agreement, the Merger and the other transactions contemplated by the Merger Agreement, and, (B) without limitation of the preceding clause (A), approval of any proposal to adjourn or postpone the Partnership Unitholders Meeting to a later date if there are not sufficient votes for approval and adoption of the Merger Agreement on the date on which the Partnership Unitholders Meeting is held; and (ii) against any Alternative Proposal and against any other action, agreement or transaction involving the Partnership that is intended, or would reasonably be expected, to prevent, impede, interfere with, delay, postpone, discourage or otherwise impair the consummation of the Merger or the other transactions contemplated by the Merger Agreement; and (iii) against any other action or agreement that would result in a breach of any obligation of the Partnership in the Merger Agreement. Each Unitholder shall retain at all times the right to vote the Subject Units in such Unitholder’s sole discretion, and without any other limitation, on any matters other than those set forth in this Section 1.1 that are at any time or from time to time presented for consideration to the Partnership’s unitholders generally.

ARTICLE II  REPRESENTATIONS AND WARRANTIES OF THE UNITHOLDERS

Each Unitholder represents and warrants, on its own account with respect to the Subject Units, to the Parent Entities as to such Unitholder on a several basis, that:

2.1          Authorization; Binding Agreement. Such Unitholder is duly organized and validly existing in good standing under the Laws of the jurisdiction in which it is incorporated or constituted and the consummation of the transactions contemplated hereby are within such Unitholder’s entity powers and have been duly authorized by all necessary entity actions on the part of such Unitholder, and such Unitholder has full power and authority to execute, deliver and perform this Agreement and to consummate the transactions contemplated hereby. This Agreement has been duly and validly executed and delivered by such Unitholder and constitutes a valid and binding obligation of such Unitholder enforceable against such Unitholder in accordance with its terms, subject to the effects of bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and other similar Laws relating to or affecting creditors’ rights generally and general equitable principles (whether considered in a proceeding in equity or at law).

2.2          Non-Contravention. Neither the execution and delivery of this Agreement by such Unitholder nor the consummation by such Unitholder of the transactions contemplated hereby, nor compliance by such Unitholder with any of the terms or provisions of this Agreement, will (i) conflict with or violate any provision of the certificate of incorporation or bylaws (or other similar governing documents), (ii) (x) violate any Law, judgment, writ or injunction of any Governmental Authority applicable to such Unitholder or any of their

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respective properties or assets, or (y) violate, conflict with, result in the loss of any benefit under, constitute a default (or an event which, with notice or lapse of time, or both, would constitute a default) under, result in the termination of or a right of termination or cancellation under, accelerate the performance required by, or result in the creation of any Lien upon any of the respective properties or assets of, such Unitholder under, any of the terms, conditions or provisions of any loan or credit agreement, debenture, note, bond, mortgage, indenture, deed of trust, license, lease, contract or other agreement, instrument or obligation, to which such Unitholder is a party, or by which they or any of their respective properties or assets may be bound or affected or (iii) result in the exercisability of any right to purchase or acquire any asset of such Unitholder, except, in the case of clauses (ii)(x), (ii)(y) and (iii), for such violations, conflicts, losses, defaults, terminations, cancellations, accelerations, Liens, purchases or acquisitions as, individually or in the aggregate, would not prevent or materially impair the consummation of the transactions contemplated hereby.

2.3          Ownership of Subject Units; Total Units. Such Unitholder is the discretionary investment adviser, manager or general partner with respect to various record and beneficial owners (as defined in Rule 13d-3 under the Exchange Act) of all such Unitholder’s Subject Units. The respective owners of the Subject Units for which the Unitholder is the investment adviser, manager or general partner has good and marketable title to all such Subject Units free and clear of any Liens, except for any such Lien that may be imposed pursuant to (i) this Agreement, (ii) the Partnership Agreement, (iii) any applicable restrictions on transfer under the Securities Act or any state securities law, or (iv) any leverage transactions pursuant to which the Subject Units serve as collateral (collectively, “Permitted Liens”). The Common Units listed on Schedule A opposite such Unitholder’s name constitute all of the Common Units beneficially owned as of the Record Date by the respective owners of the Subject Units for which the Unitholder is the investment adviser or general partner.

2.4          Voting Power. Such Unitholder has full voting power with respect to all such Unitholder’s Subject Units, and full power of disposition, full power to issue instructions with respect to the matters set forth herein and full power to agree to all of the matters set forth in this Agreement, in each case with respect to all such Unitholder’s Subject Units. None of such Unitholder’s Subject Units are subject to any unitholders’ agreement, proxy, voting trust or other agreement or arrangement with respect to the voting of such Subject Units, except as provided hereunder.

2.5          Absence of Litigation. With respect to such Unitholder, as of the date hereof, there is no Proceeding pending against, or, to the actual knowledge of such Unitholder, threatened in writing against such Unitholder or any of such Unitholder’s properties or assets (including any Subject Units beneficially owned by such Unitholder) before or by any Governmental Authority that could reasonably be expected to prevent or materially delay or impair the consummation by such Unitholder of the transactions contemplated by this Agreement or otherwise materially impair such Unitholder’s ability to perform its obligations hereunder.

2.6          Brokers. No broker, finder, financial advisor, investment banker or other Person is entitled to any brokerage, finder’s, financial advisor’s or other similar fee or commission from

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the Parent Entities or the Partnership in connection with the transactions contemplated hereby based upon arrangements made by or on behalf of such Unitholder.

ARTICLE III
REPRESENTATIONS AND WARRANTIES OF THE PARENT ENTITIES

The Parent Entities represent and warrant to the Unitholders that:

3.1          Organization and Qualification. Each of the Parent Entities is a duly organized and validly existing entity in good standing under the Laws of the jurisdiction of its organization. All of the issued and outstanding capital stock of Merger Sub is owned directly or indirectly by Parent.

3.2          Authority for this Agreement. Each of the Parent Entities has all requisite entity power and authority to execute, deliver and perform its obligations under this Agreement and to consummate the transactions contemplated hereby. The execution and delivery of this Agreement by the Parent Entities have been duly and validly authorized by all necessary entity action on the part of each of the Parent Entities, and no other entity proceedings on the part of the Parent Entities are necessary to authorize this Agreement. This Agreement has been duly and validly executed and delivered by the Parent Entities and, assuming the due authorization, execution and delivery by the Unitholders, constitutes a legal, valid and binding obligation of each of the Parent Entities, enforceable against each of the Parent Entities in accordance with its terms, except as enforceability may be limited by bankruptcy Laws, other similar Laws affecting creditors’ rights and general principles of equity affecting the availability of specific performance and other equitable remedies.

ARTICLE IV
MISCELLANEOUS

4.1          Documentation and Information. Such Unitholder shall not make any public announcement regarding this Agreement and the transactions contemplated hereby without the prior written consent of Parent (such consent not to be unreasonably withheld, conditioned or delayed), except as may be required by applicable Law (provided that reasonable notice of any such disclosure will be provided to Parent).  Parent acknowledges it has been advised by each Unitholder of an obligation and intent of that Unitholder to file a Schedule 13D with the SEC with respect to the Unitholder’s obligations under this Agreement, and Parent consents to that filing.  Such Unitholder consents to and hereby authorizes the Parent Entities and the Partnership to publish and disclose in all documents and schedules filed with the SEC or other Governmental Authority or applicable securities exchange, to the extent Parent determines such filing is required by applicable Law or regulation, and any press release or other disclosure document that the Parent Entities reasonably determine to be necessary or advisable in connection with the Merger and any other transactions contemplated by the Merger Agreement, such Unitholder’s identity and ownership of the Subject Units, the existence of this Agreement and the nature of such Unitholder’s commitments and obligations under this Agreement, and such Unitholder acknowledges that the Parent Entities and the Partnership may, in their respective sole discretion, file this Agreement or a form hereof with the SEC or any other Governmental Authority or securities exchange.  For the avoidance of doubt, no consent of the Unitholder shall be required

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to file and accurately describe contracts to which any Unitholder is a party or is otherwise referenced therein in compliance with Parent’s reporting obligations under the Securities Exchange Act of 1934. Such Unitholder agrees to promptly give Parent and the Partnership any information it may reasonably require for the preparation of any such disclosure documents, and such Unitholder agrees to promptly notify Parent and the Partnership, as applicable, of any required corrections with respect to any written information supplied by such Unitholder specifically for use in any such disclosure document, if and to the extent that any such information shall have become false or misleading in any material respect.

4.2          Notices. Any and all notices or other communications or deliveries required or permitted to be provided hereunder will be in writing and sent by facsimile, by electronic mail, by nationally recognized overnight courier service or by registered mail and will be deemed given and effective on the earliest of (a) the date of transmission, if such notice or communication is delivered via electronic mail at the email address specified in Section 8.9 of the Merger Agreement or facsimile at the facsimile telephone number specified in Section 8.9 of the Merger Agreement, in either case, prior to 5:00 p.m. (New York City time) on a Business Day and, in each case, a copy is sent on such Business Day by nationally recognized overnight courier service, (b) the Business Day after the date of transmission, if such notice or communication is delivered via electronic mail at the email address specified in Section 8.9 of the Merger Agreement or facsimile at the facsimile telephone number specified in Section 8.9 of the Merger Agreement, in each case, later than 5:00 p.m. (New York City time) on any date and earlier than 12 midnight (New York City time) on the following date and a copy is sent no later than such date by nationally recognized overnight courier service, (c) when received, if sent by nationally recognized overnight courier service (other than in the cases of clauses (a) and (b) above), or (d) upon actual receipt by the party to whom such notice is required to be given if sent by registered mail. The address for such notices and communications will be as set forth (i) if to any Parent Entity, to the address or facsimile number set forth in Section 8.9 of the Merger Agreement and (ii) if to a Unitholder, to such Unitholder’s address or facsimile number set forth on a signature page hereto, or to such other address or facsimile number as such party may hereafter specify for the purpose by notice to each other party hereto.

4.3          Termination. This Agreement shall terminate automatically with respect to a Unitholder, without any notice or other action by any Person, upon the first to occur of (a) the valid termination of the Merger Agreement in accordance with its terms, (b) the Effective Time, (c) the entry without the prior written consent of such Unitholder into any amendment or modification to the Merger Agreement or any waiver of any of the Partnership’s rights under the Merger Agreement, in each case, that results in a decrease in the Exchange Ratio or Cash Consideration (in each case, as defined in the Merger Agreement on the date hereof), or (d) the mutual written consent of Parent and such Unitholder (the date of termination with respect to any Unitholder being referred to herein as the “Termination Date”). Upon termination of this Agreement, no party shall have any further obligations or liabilities under this Agreement; provided, however, that (x) nothing set forth in this Section 4.3 shall relieve any party from liability for any breach of this Agreement prior to termination hereof and (y) the provisions of this Article IV shall survive any termination of this Agreement.

4.4          Amendments and Waivers. Any provision of this Agreement may be amended or waived if such amendment or waiver is in writing and is signed, in the case of an amendment,

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by each party to this Agreement or, in the case of a waiver, by each party against whom the waiver is to be effective. No failure or delay by any party in exercising any right hereunder will operate as a waiver thereof nor will any single or partial exercise thereof preclude any other or further exercise thereof or the exercise of any other right.

4.5          Expenses. All fees and expenses incurred in connection herewith and the transactions contemplated hereby shall be paid by the party incurring such fees and expenses, whether or not the Merger is consummated.

4.6          Assignment. Neither this Agreement nor any of the rights, interests or obligations hereunder may be assigned, in whole or in part, by operation of Law or otherwise, by any of the parties without the prior written consent of the other parties, except that Merger Sub may assign, in its sole discretion, any of or all its rights, interests and obligations under this Agreement to any wholly owned Subsidiary of Parent, but no such assignment will relieve Parent, Parent GP or Merger Sub of any of its obligations hereunder. Subject to the preceding sentence, this Agreement will be binding upon, inure to the benefit of, and be enforceable by, the parties hereto and their respective successors and permitted assigns. Any purported assignment not permitted under this Section 4.6 will be null and void.

4.7          Counterparts. This Agreement may be executed in counterparts (each of which will be deemed to be an original but all of which taken together will constitute one and the same agreement) and will become effective when one or more counterparts have been signed by each of the parties and delivered to the other parties.

4.8          Entire Agreement; No Third-Party Beneficiaries. This Agreement, together with Schedule A, and the other documents and certificates delivered pursuant hereto, (a) constitute the entire agreement, and supersede all other prior agreements and understandings, both written and oral, among the parties with respect to the subject matter of this Agreement and thereof and (b) will not confer upon any Person other than the parties hereto any rights (including third-party beneficiary rights or otherwise) or remedies hereunder.

4.9          Governing Law; Jurisdiction; Waiver of Jury Trial.

(a)           This Agreement will be governed by, and construed in accordance with, the laws of the State of Delaware, applicable to contracts executed in and to be performed entirely within that State.

(b)           Each of the parties hereto irrevocably agrees that any legal action or proceeding with respect to this Agreement and the rights and obligations arising hereunder, or for recognition and enforcement of any judgment in respect of this Agreement and the rights and obligations arising hereunder brought by the other party hereto or its successors or assigns, will be brought and determined exclusively in the Delaware Court of Chancery and any state appellate court therefrom within the State of Delaware (or, if the Delaware Court of Chancery declines to accept jurisdiction over a particular matter, any state or federal court within the State of Delaware). Each of the parties hereto hereby irrevocably submits with regard to any such action or proceeding for itself and in respect of its property, generally and unconditionally, to the personal jurisdiction of the aforesaid courts and agrees that it will not bring any action relating to

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this Agreement or any of the transactions contemplated by this Agreement in any court other than the aforesaid courts. Each of the parties hereto hereby irrevocably waives, and agrees not to assert as a defense, counterclaim or otherwise, in any action or proceeding with respect to this Agreement, (i) any claim that it is not personally subject to the jurisdiction of the above named courts for any reason, (ii) any claim that it or its property is exempt or immune from the jurisdiction of any such court or from any legal process commenced in such courts (whether through service of notice, attachment prior to judgment, attachment in aid of execution of judgment, execution of judgment or otherwise) and (iii) to the fullest extent permitted by the applicable Law, any claim that (x) the suit, action or proceeding in such court is brought in an inconvenient forum, (y) the venue of such suit, action or proceeding is improper or (z) this Agreement, or the subject matter hereof, may not be enforced in or by such courts. The parties hereto further agree that the mailing by certified or registered mail, return receipt requested, (i) if to any Parent Entity, to the address or facsimile number set forth in Section 8.9 of the Merger Agreement and (ii) if to a Unitholder, to such Unitholder’s address set forth on a signature page hereto, or to such other address as such party may hereafter specify for the purpose by notice to each other party hereto, of any process required by any such court will constitute valid and lawful service of process against them, without necessity for service by any other means provided by statute or rule of court.

(c)           EACH PARTY HEREBY IRREVOCABLY WAIVES ALL RIGHT TO TRIAL BY JURY IN ANY ACTION, PROCEEDING OR COUNTERCLAIM (WHETHER BASED ON CONTRACT, TORT OR OTHERWISE) ARISING OUT OF OR RELATING TO THIS AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY OR THE ACTIONS OF ANY PARTY IN THE NEGOTIATION, ADMINISTRATION, PERFORMANCE AND ENFORCEMENT OF THIS AGREEMENT AND THE TRANSACTIONS CONTEMPLATED BY THIS AGREEMENT.

4.10        Specific Enforcement. The parties agree that irreparable damage would occur and that the parties would not have any adequate remedy at law in the event that any of the provisions of this Agreement were not performed in accordance with their specific terms or were otherwise breached and it is accordingly agreed that the parties will be entitled to an injunction or injunctions to prevent breaches of this Agreement and to enforce specifically the terms and provisions of this Agreement, in each case, in accordance with this Section 4.10 in the Delaware Court of Chancery or any federal court sitting in the State of Delaware, this being in addition to any other remedy to which they are entitled at law or in equity. Each of the parties agrees that it will not oppose the granting of an injunction, specific performance and other equitable relief as provided herein on the basis that (x) either party has an adequate remedy at law or (y) an award of specific performance is not an appropriate remedy for any reason at law or equity. Each party further agrees that no party will be required to obtain, furnish or post any bond or similar instrument in connection with or as a condition to obtaining any remedy referred to in this Section 4.10, and each party irrevocably waives any right it may have to require the obtaining, furnishing or posting of any such bond or similar instrument.

4.11        Severability. If any term or other provision of this Agreement is determined by a court of competent jurisdiction to be invalid, illegal or incapable of being enforced by any rule of Law or public policy, all other terms, provisions and conditions of this Agreement will nevertheless remain in full force and effect. Upon such determination that any term or other

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provision is invalid, illegal or incapable of being enforced, the parties hereto will negotiate in good faith to modify this Agreement so as to effect the original intent of the parties as closely as possible to the fullest extent permitted by Applicable Law in an acceptable manner to the end that the transactions contemplated hereby are fulfilled to the extent possible.

4.12        Interpretation.

(a)           The headings contained in this Agreement are for reference purposes only and will not affect in any way the meaning or interpretation of this Agreement. Whenever the words “include,” “includes” or “including” are used in this Agreement, they will be deemed to be followed by the words “without limitation.” The words “hereof,” “herein” and “hereunder” and words of similar import when used in this Agreement will refer to this Agreement as a whole and not to any particular provision of this Agreement. All terms defined in this Agreement will have the defined meanings when used in any certificate or other document made or delivered pursuant hereto unless otherwise defined therein. The definitions contained in this Agreement are applicable to the singular as well as the plural forms of such terms and to the masculine as well as to the feminine and neuter genders of such term. Any agreement, instrument or statute defined or referred to herein or in any agreement or instrument that is referred to herein means such agreement, instrument or statute as from time to time amended, modified or supplemented, including (in the case of agreements or instruments) by waiver or consent and (in the case of statutes) by succession of comparable successor statutes and references to all attachments thereto and instruments incorporated therein. References to a Person are also to its permitted successors and assigns.

(b)           The parties hereto have participated jointly in the negotiation and drafting of this Agreement with the assistance of counsel and other advisors and, in the event an ambiguity or question of intent or interpretation arises, this Agreement will be construed as jointly drafted by the parties hereto and no presumption or burden of proof will arise favoring or disfavoring any party by virtue of the authorship of any provision of this Agreement or interim drafts of this Agreement.

4.13        Further Assurances. Each Unitholder will execute and deliver, or cause to be executed and delivered, all further documents and instruments and use its reasonable best efforts to take, or cause to be taken, all actions and to do, or cause to be done, all things necessary, proper or advisable under applicable Laws and regulations, to perform its obligations under this Agreement.

4.14        Unitholder Obligation Several and Not Joint. The obligations of each Unitholder hereunder shall be several and not joint, and no Unitholder shall be liable for any breach of the terms of this Agreement by any other Unitholder.

[Remainder of Page Intentionally Left Blank. Signature Pages Follow.]

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The parties are executing this Agreement on the date set forth in the introductory clause.

PARENT:
MPLX LP
By:	MPLX GP LLC,
	its general partner
By:	/s/ G.R. Heminger
Name: G.R. Heminger
Title: Chairman and Chief Executive Officer
PARENT GP:
MPLX GP LLC
By:	/s/ G.R. Heminger
	Name: G.R. Heminger
	Title: Chairman and Chief Executive Officer
MERGER SUB:
SAPPHIRE HOLDCO LLC
By:	/s/ P.K.M. Beall
Name: P.K.M. Beall
Title: President

[Signature Page to Voting Agreement]

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UNITHOLDER
KAYNE ANDERSON CAPITAL ADVISORS, L.P., as investment adviser, manager or general partner
By:	/s/ David Shladovsky
Name: David Shladovsky
Title: General Counsel
UNITHOLDER
KA FUND ADVISORS, LLC, as investment adviser, manager or general partner
By:		/s/ James Baker
Name: James Baker
Title: Managing Director

[Signature Page to Voting Agreement]

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Schedule A

Name of Unitholder; Address	Number of Common Units
Kayne Anderson Capital Advisors, L.P. 1800 Avenue of the Stars, 3rd Floor Los Angeles, CA 90067 E-mail address: dshladovsky@kaynecapital.com and jbaker@kaynecapital.com	2,792,961
KA Fund Advisors, LLC 811 Main Street, 14th Floor Houston, TX 77002 dshladovsky@kaynecapital.com and jbaker@kaynecapital.com	8,344,758

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EX-99.3

Exhibit 99.3

VOTING AGREEMENT

This VOTING AGREEMENT (this “Agreement”), dated as of November 16, 2015, is entered into by and among MPLX LP, a Delaware limited partnership (“Parent”), MPLX GP LLC, a Delaware limited liability company and the general partner of Parent (“Parent GP”), and Sapphire Holdco LLC, a Delaware limited liability company and a wholly owned subsidiary of Parent (“Merger Sub” and, with Parent and Parent GP, the “Parent Entities”), and each of the Persons set forth on Schedule A hereto (each, a “Unitholder”), as investment adviser, manager or general partner on behalf of various record and beneficial owners. All terms used but not otherwise defined in this Agreement shall have the respective meanings ascribed to such terms in the Merger Agreement (as defined below).

WHEREAS, as of the date hereof, each Unitholder is the discretionary investment adviser, manager or general partner with respect to various record and beneficial owners (as defined in Rule 13d-3 under the Exchange Act) that own and have delegated voting authority to such Unitholder with respect to, the aggregate number of Common Units set forth opposite such Unitholder’s name on Schedule A (all such units set forth on Schedule A next to the Unitholder’s name specify those units held as of October 5, 2015, which is the record date for holders of Common Units entitled to vote on the transactions contemplated by the Merger Agreement and is referred to as the “Record Date”) and for which Unitholder continues to have voting power as of the date hereof, but excluding any Common Units over which the Unitholder ceases to having voting power subsequent to the date of this Agreement (including any such Common Units as may be included on Schedule A) (all such units being referred to herein as the “Subject Units”); and

WHEREAS,  the Parent Entities, Marathon Petroleum Corporation, a Delaware corporation and the ultimate parent of Parent GP (“MPC”), and MarkWest Energy Partners, L.P., a Delaware limited partnership (the “Partnership”), have entered into an Agreement and Plan of Merger, dated July 11, 2015, as amended on November 10, 2015 (as it may be further amended pursuant to the terms thereof, including pursuant to the Amendment (as defined below), the “Merger Agreement”), which provides, among other things, for the merger of Merger Sub with and into the Partnership, upon the terms and subject to the conditions set forth therein (the “Merger”) in accordance with the DRULPA, whereby each issued and outstanding Common Unit will be converted into the right to receive the consideration set forth in the Merger Agreement;

WHEREAS, concurrently with the execution and delivery hereof, the Parent Entities, MPC and the Partnership are entering into Amendment No. 2 to the Agreement and Plan of Merger (the “Amendment”), providing for an Exchange Ratio of 1.09 Parent Units and cash in an amount of $6.20 per Common Unit (the “Specified Consideration”);

NOW, THEREFORE, in consideration of the foregoing and the respective representations, warranties, covenants and agreements set forth below and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto, intending to be legally bound, do hereby agree as follows:

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ARTICLE I
AGREEMENT TO VOTE

1.1          Agreement to Vote. Subject to the terms of this Agreement, and so long as the Unitholders remain entitled to receive not less than the Specified Consideration, each Unitholder hereby irrevocably and unconditionally agrees that, after the date hereof and until the Termination Date with respect to such Unitholder, at any annual or special meeting of the unitholders of the Partnership, however called, including any adjournment or postponement thereof, and in connection with any action proposed to be taken by written consent of the unitholders of the Partnership, such Unitholder shall, in each case to the fullest extent that such Unitholder’s Subject Units are entitled to vote thereon and Unitholder continues to have voting power over such Subject Units: (a) appear at each such meeting or otherwise cause all such Subject Units to be counted as present thereat for purposes of determining a quorum; and (b) vote (or cause to be voted), or deliver (or cause to be delivered) a written consent with respect to, all of its Subject Units (i) in favor of the (A) approval of the Merger Agreement, the Merger and the other transactions contemplated by the Merger Agreement, and, (B) without limitation of the preceding clause (A), approval of any proposal to adjourn or postpone the Partnership Unitholders Meeting to a later date if there are not sufficient votes for approval and adoption of the Merger Agreement on the date on which the Partnership Unitholders Meeting is held; and (ii) against any Alternative Proposal and against any other action, agreement or transaction involving the Partnership that is intended, or would reasonably be expected, to prevent, impede, interfere with, delay, postpone, discourage or otherwise impair the consummation of the Merger or the other transactions contemplated by the Merger Agreement; and (iii) against any other action or agreement that would result in a breach of any obligation of the Partnership in the Merger Agreement. Each Unitholder shall retain at all times the right to vote the Subject Units in such Unitholder’s sole discretion, and without any other limitation, on any matters other than those set forth in this Section 1.1 that are at any time or from time to time presented for consideration to the Partnership’s unitholders generally.

ARTICLE II  REPRESENTATIONS AND WARRANTIES OF THE UNITHOLDERS

Each Unitholder represents and warrants, on its own account with respect to the Subject Units, to the Parent Entities as to such Unitholder on a several basis, that:

2.1          Authorization; Binding Agreement. Such Unitholder is duly organized and validly existing in good standing under the Laws of the jurisdiction in which it is incorporated or constituted and the consummation of the transactions contemplated hereby are within such Unitholder’s entity powers and have been duly authorized by all necessary entity actions on the part of such Unitholder, and such Unitholder has full power and authority to execute, deliver and perform this Agreement and to consummate the transactions contemplated hereby. This Agreement has been duly and validly executed and delivered by such Unitholder and constitutes a valid and binding obligation of such Unitholder enforceable against such Unitholder in accordance with its terms, subject to the effects of bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and other similar Laws relating to or affecting creditors’ rights generally and general equitable principles (whether considered in a proceeding in equity or at law).

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2.2          Non-Contravention. Neither the execution and delivery of this Agreement by such Unitholder nor the consummation by such Unitholder of the transactions contemplated hereby, nor compliance by such Unitholder with any of the terms or provisions of this Agreement, will (i) conflict with or violate any provision of the certificate of incorporation or bylaws (or other similar governing documents), (ii) (x) violate any Law, judgment, writ or injunction of any Governmental Authority applicable to such Unitholder or any of their respective properties or assets, or (y) violate, conflict with, result in the loss of any benefit under, constitute a default (or an event which, with notice or lapse of time, or both, would constitute a default) under, result in the termination of or a right of termination or cancellation under, accelerate the performance required by, or result in the creation of any Lien upon any of the respective properties or assets of, such Unitholder under, any of the terms, conditions or provisions of any loan or credit agreement, debenture, note, bond, mortgage, indenture, deed of trust, license, lease, contract or other agreement, instrument or obligation, to which such Unitholder is a party, or by which they or any of their respective properties or assets may be bound or affected or (iii) result in the exercisability of any right to purchase or acquire any asset of such Unitholder, except, in the case of clauses (ii)(x), (ii)(y) and (iii), for such violations, conflicts, losses, defaults, terminations, cancellations, accelerations, Liens, purchases or acquisitions as, individually or in the aggregate, would not prevent or materially impair the consummation of the transactions contemplated hereby.

2.3          Ownership of Subject Units; Total Units. Such Unitholder is the discretionary investment adviser, manager or general partner with respect to various record and beneficial owners (as defined in Rule 13d-3 under the Exchange Act) of all such Unitholder’s Subject Units. To the knowledge of Unitholder, the respective owners of the Subject Units for which the Unitholder is the investment adviser or general partner has good and marketable title to all such Subject Units free and clear of any Liens, except for any such Lien that may be imposed pursuant to (i) this Agreement, (ii) the Partnership Agreement, (iii) any applicable restrictions on transfer under the Securities Act or any state securities law, or (iv) any leverage transactions pursuant to which the Subject Units serve as collateral (collectively, “Permitted Liens”). The Common Units listed on Schedule A opposite such Unitholder’s name constitute all of the Common Units beneficially owned as of the Record Date by the respective owners of the Subject Units for which the Unitholder is the investment adviser or general partner and for which the Unitholder has voting power.

2.4          Voting Power. Such Unitholder has full voting power with respect to all such Unitholder’s Subject Units, and full power of disposition, full power to issue instructions with respect to the matters set forth herein and full power to agree to all of the matters set forth in this Agreement, in each case with respect to all such Unitholder’s Subject Units. None of such Unitholder’s Subject Units are subject to any unitholders’ agreement, proxy, voting trust or other agreement or arrangement with respect to the voting of such Subject Units, except as provided hereunder.

2.5          Absence of Litigation. With respect to such Unitholder, as of the date hereof, there is no Proceeding pending against, or, to the actual knowledge of such Unitholder, threatened in writing against such Unitholder or any of such Unitholder’s properties or assets (including any Subject Units beneficially owned by such Unitholder) before or by any

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Governmental Authority that could reasonably be expected to prevent or materially delay or impair the consummation by such Unitholder of the transactions contemplated by this Agreement or otherwise materially impair such Unitholder’s ability to perform its obligations hereunder.

2.6          Brokers. No broker, finder, financial advisor, investment banker or other Person is entitled to any brokerage, finder’s, financial advisor’s or other similar fee or commission from the Parent Entities or the Partnership in connection with the transactions contemplated hereby based upon arrangements made by or on behalf of such Unitholder.

ARTICLE III
REPRESENTATIONS AND WARRANTIES OF THE PARENT ENTITIES

The Parent Entities represent and warrant to the Unitholders that:

3.1          Organization and Qualification. Each of the Parent Entities is a duly organized and validly existing entity in good standing under the Laws of the jurisdiction of its organization. All of the issued and outstanding capital stock of Merger Sub is owned directly or indirectly by Parent.

3.2          Authority for this Agreement. Each of the Parent Entities has all requisite entity power and authority to execute, deliver and perform its obligations under this Agreement and to consummate the transactions contemplated hereby. The execution and delivery of this Agreement by the Parent Entities have been duly and validly authorized by all necessary entity action on the part of each of the Parent Entities, and no other entity proceedings on the part of the Parent Entities are necessary to authorize this Agreement. This Agreement has been duly and validly executed and delivered by the Parent Entities and, assuming the due authorization, execution and delivery by the Unitholders, constitutes a legal, valid and binding obligation of each of the Parent Entities, enforceable against each of the Parent Entities in accordance with its terms, except as enforceability may be limited by bankruptcy Laws, other similar Laws affecting creditors’ rights and general principles of equity affecting the availability of specific performance and other equitable remedies.

ARTICLE IV
MISCELLANEOUS

4.1          Documentation and Information. Such Unitholder shall not make any public announcement regarding this Agreement and the transactions contemplated hereby without the prior written consent of Parent (such consent not to be unreasonably withheld, conditioned or delayed), except as may be required by applicable Law (provided that reasonable notice of any such disclosure will be provided to Parent).  Parent acknowledges it has been advised by each Unitholder of an obligation and intent of that Unitholder to file a Schedule 13D with the SEC with respect to the Unitholder’s obligations under this Agreement, and Parent consents to that filing.  Such Unitholder consents to and hereby authorizes the Parent Entities and the Partnership to publish and disclose in all documents and schedules filed with the SEC or other Governmental Authority or applicable securities exchange, to the extent Parent determines such filing is required by applicable Law or regulation, and any press release or other disclosure document that the Parent Entities reasonably determine to be necessary or advisable in connection with the

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Merger and any other transactions contemplated by the Merger Agreement, such Unitholder’s identity and beneficial ownership of the Subject Units, the existence of this Agreement and the nature of such Unitholder’s commitments and obligations under this Agreement, and such Unitholder acknowledges that the Parent Entities and the Partnership may, in their respective sole discretion, file this Agreement or a form hereof with the SEC or any other Governmental Authority or securities exchange.  For the avoidance of doubt, no consent of the Unitholder shall be required to file and accurately describe contracts to which any Unitholder is a party or is otherwise referenced therein in compliance with Parent’s reporting obligations under the Securities Exchange Act of 1934. Such Unitholder agrees to promptly give Parent and the Partnership any information it may reasonably require for the preparation of any such disclosure documents, and such Unitholder agrees to promptly notify Parent and the Partnership, as applicable, of any required corrections with respect to any written information supplied by such Unitholder specifically for use in any such disclosure document, if and to the extent that any such information shall have become false or misleading in any material respect.

4.2          Notices. Any and all notices or other communications or deliveries required or permitted to be provided hereunder will be in writing and sent by facsimile, by electronic mail, by nationally recognized overnight courier service or by registered mail and will be deemed given and effective on the earliest of (a) the date of transmission, if such notice or communication is delivered via electronic mail at the email address specified in Section 8.9 of the Merger Agreement or facsimile at the facsimile telephone number specified in Section 8.9 of the Merger Agreement, in either case, prior to 5:00 p.m. (New York City time) on a Business Day and, in each case, a copy is sent on such Business Day by nationally recognized overnight courier service, (b) the Business Day after the date of transmission, if such notice or communication is delivered via electronic mail at the email address specified in Section 8.9 of the Merger Agreement or facsimile at the facsimile telephone number specified in Section 8.9 of the Merger Agreement, in each case, later than 5:00 p.m. (New York City time) on any date and earlier than 12 midnight (New York City time) on the following date and a copy is sent no later than such date by nationally recognized overnight courier service, (c) when received, if sent by nationally recognized overnight courier service (other than in the cases of clauses (a) and (b) above), or (d) upon actual receipt by the party to whom such notice is required to be given if sent by registered mail. The address for such notices and communications will be as set forth (i) if to any Parent Entity, to the address or facsimile number set forth in Section 8.9 of the Merger Agreement and (ii) if to a Unitholder, to such Unitholder’s address or facsimile number set forth on a signature page hereto, or to such other address or facsimile number as such party may hereafter specify for the purpose by notice to each other party hereto.

4.3          Termination. This Agreement shall terminate automatically with respect to a Unitholder, without any notice or other action by any Person, upon the first to occur of (a) the valid termination of the Merger Agreement in accordance with its terms, (b) the Effective Time, (c) the entry without the prior written consent of such Unitholder into any amendment or modification to the Merger Agreement or any waiver of any of the Partnership’s rights under the Merger Agreement, in each case, that results in a decrease in the Exchange Ratio or Cash Consideration (in each case, as defined in the Merger Agreement on the date hereof), or (d) the mutual written consent of Parent and such Unitholder (the date of termination with respect to any Unitholder being referred to herein as the “Termination Date”). Upon termination of this Agreement, no party shall have any further obligations or liabilities under this

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Agreement; provided, however, that (x) nothing set forth in this Section 4.3 shall relieve any party from liability for any breach of this Agreement prior to termination hereof and (y) the provisions of this Article IV shall survive any termination of this Agreement.

4.4          Amendments and Waivers. Any provision of this Agreement may be amended or waived if such amendment or waiver is in writing and is signed, in the case of an amendment, by each party to this Agreement or, in the case of a waiver, by each party against whom the waiver is to be effective. No failure or delay by any party in exercising any right hereunder will operate as a waiver thereof nor will any single or partial exercise thereof preclude any other or further exercise thereof or the exercise of any other right.

4.5          Expenses. All fees and expenses incurred in connection herewith and the transactions contemplated hereby shall be paid by the party incurring such fees and expenses, whether or not the Merger is consummated.

4.6          Assignment. Neither this Agreement nor any of the rights, interests or obligations hereunder may be assigned, in whole or in part, by operation of Law or otherwise, by any of the parties without the prior written consent of the other parties, except that Merger Sub may assign, in its sole discretion, any of or all its rights, interests and obligations under this Agreement to any wholly owned Subsidiary of Parent, but no such assignment will relieve Parent, Parent GP or Merger Sub of any of its obligations hereunder. Subject to the preceding sentence, this Agreement will be binding upon, inure to the benefit of, and be enforceable by, the parties hereto and their respective successors and permitted assigns. Any purported assignment not permitted under this Section 4.6 will be null and void.

4.7          Counterparts. This Agreement may be executed in counterparts (each of which will be deemed to be an original but all of which taken together will constitute one and the same agreement) and will become effective when one or more counterparts have been signed by each of the parties and delivered to the other parties.

4.8          Entire Agreement; No Third-Party Beneficiaries. This Agreement, together with Schedule A, and the other documents and certificates delivered pursuant hereto, (a) constitute the entire agreement, and supersede all other prior agreements and understandings, both written and oral, among the parties with respect to the subject matter of this Agreement and thereof and (b) will not confer upon any Person other than the parties hereto any rights (including third-party beneficiary rights or otherwise) or remedies hereunder.

4.9          Governing Law; Jurisdiction; Waiver of Jury Trial.

(a)           This Agreement will be governed by, and construed in accordance with, the laws of the State of Delaware, applicable to contracts executed in and to be performed entirely within that State.

(b)           Each of the parties hereto irrevocably agrees that any legal action or proceeding with respect to this Agreement and the rights and obligations arising hereunder, or for recognition and enforcement of any judgment in respect of this Agreement and the rights and obligations arising hereunder brought by the other party hereto or its successors or assigns, will be brought and determined exclusively in the Delaware Court of Chancery and any state

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appellate court therefrom within the State of Delaware (or, if the Delaware Court of Chancery declines to accept jurisdiction over a particular matter, any state or federal court within the State of Delaware). Each of the parties hereto hereby irrevocably submits with regard to any such action or proceeding for itself and in respect of its property, generally and unconditionally, to the personal jurisdiction of the aforesaid courts and agrees that it will not bring any action relating to this Agreement or any of the transactions contemplated by this Agreement in any court other than the aforesaid courts. Each of the parties hereto hereby irrevocably waives, and agrees not to assert as a defense, counterclaim or otherwise, in any action or proceeding with respect to this Agreement, (i) any claim that it is not personally subject to the jurisdiction of the above named courts for any reason, (ii) any claim that it or its property is exempt or immune from the jurisdiction of any such court or from any legal process commenced in such courts (whether through service of notice, attachment prior to judgment, attachment in aid of execution of judgment, execution of judgment or otherwise) and (iii) to the fullest extent permitted by the applicable Law, any claim that (x) the suit, action or proceeding in such court is brought in an inconvenient forum, (y) the venue of such suit, action or proceeding is improper or (z) this Agreement, or the subject matter hereof, may not be enforced in or by such courts. The parties hereto further agree that the mailing by certified or registered mail, return receipt requested, (i) if to any Parent Entity, to the address or facsimile number set forth in Section 8.9 of the Merger Agreement and (ii) if to a Unitholder, to such Unitholder’s address set forth on a signature page hereto, or to such other address as such party may hereafter specify for the purpose by notice to each other party hereto, of any process required by any such court will constitute valid and lawful service of process against them, without necessity for service by any other means provided by statute or rule of court.

(c)           EACH PARTY HEREBY IRREVOCABLY WAIVES ALL RIGHT TO TRIAL BY JURY IN ANY ACTION, PROCEEDING OR COUNTERCLAIM (WHETHER BASED ON CONTRACT, TORT OR OTHERWISE) ARISING OUT OF OR RELATING TO THIS AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY OR THE ACTIONS OF ANY PARTY IN THE NEGOTIATION, ADMINISTRATION, PERFORMANCE AND ENFORCEMENT OF THIS AGREEMENT AND THE TRANSACTIONS CONTEMPLATED BY THIS AGREEMENT.

4.10        Specific Enforcement. The parties agree that irreparable damage would occur and that the parties would not have any adequate remedy at law in the event that any of the provisions of this Agreement were not performed in accordance with their specific terms or were otherwise breached and it is accordingly agreed that the parties will be entitled to an injunction or injunctions to prevent breaches of this Agreement and to enforce specifically the terms and provisions of this Agreement, in each case, in accordance with this Section 4.10 in the Delaware Court of Chancery or any federal court sitting in the State of Delaware, this being in addition to any other remedy to which they are entitled at law or in equity. Each of the parties agrees that it will not oppose the granting of an injunction, specific performance and other equitable relief as provided herein on the basis that (x) either party has an adequate remedy at law or (y) an award of specific performance is not an appropriate remedy for any reason at law or equity. Each party further agrees that no party will be required to obtain, furnish or post any bond or similar instrument in connection with or as a condition to obtaining any remedy referred to in this Section 4.10, and each party irrevocably waives any right it may have to require the obtaining, furnishing or posting of any such bond or similar instrument.

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4.11        Severability. If any term or other provision of this Agreement is determined by a court of competent jurisdiction to be invalid, illegal or incapable of being enforced by any rule of Law or public policy, all other terms, provisions and conditions of this Agreement will nevertheless remain in full force and effect. Upon such determination that any term or other provision is invalid, illegal or incapable of being enforced, the parties hereto will negotiate in good faith to modify this Agreement so as to effect the original intent of the parties as closely as possible to the fullest extent permitted by Applicable Law in an acceptable manner to the end that the transactions contemplated hereby are fulfilled to the extent possible.

4.12        Interpretation.

(a)           The headings contained in this Agreement are for reference purposes only and will not affect in any way the meaning or interpretation of this Agreement. Whenever the words “include,” “includes” or “including” are used in this Agreement, they will be deemed to be followed by the words “without limitation.” The words “hereof,” “herein” and “hereunder” and words of similar import when used in this Agreement will refer to this Agreement as a whole and not to any particular provision of this Agreement. All terms defined in this Agreement will have the defined meanings when used in any certificate or other document made or delivered pursuant hereto unless otherwise defined therein. The definitions contained in this Agreement are applicable to the singular as well as the plural forms of such terms and to the masculine as well as to the feminine and neuter genders of such term. Any agreement, instrument or statute defined or referred to herein or in any agreement or instrument that is referred to herein means such agreement, instrument or statute as from time to time amended, modified or supplemented, including (in the case of agreements or instruments) by waiver or consent and (in the case of statutes) by succession of comparable successor statutes and references to all attachments thereto and instruments incorporated therein. References to a Person are also to its permitted successors and assigns.

(b)           The parties hereto have participated jointly in the negotiation and drafting of this Agreement with the assistance of counsel and other advisors and, in the event an ambiguity or question of intent or interpretation arises, this Agreement will be construed as jointly drafted by the parties hereto and no presumption or burden of proof will arise favoring or disfavoring any party by virtue of the authorship of any provision of this Agreement or interim drafts of this Agreement.

4.13        Further Assurances. Each Unitholder will execute and deliver, or cause to be executed and delivered, all further documents and instruments and use its reasonable best efforts to take, or cause to be taken, all actions and to do, or cause to be done, all things necessary, proper or advisable under applicable Laws and regulations, to perform its obligations under this Agreement.

4.14        Unitholder Obligation Several and Not Joint. The obligations of each Unitholder hereunder shall be several and not joint, and no Unitholder shall be liable for any breach of the terms of this Agreement by any other Unitholder.

[Remainder of Page Intentionally Left Blank. Signature Pages Follow.]

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The parties are executing this Agreement on the date set forth in the introductory clause.

PARENT:
MPLX LP
By:	MPLX GP LLC,
	its general partner
By:	/s/ G.R. Heminger
Name: G.R. Heminger
Title: Chairman and Chief Executive Officer
PARENT GP:
MPLX GP LLC
By:	/s/ G.R. Heminger
	Name: G.R. Heminger
	Title: Chairman and Chief Executive Officer
MERGER SUB:
SAPPHIRE HOLDCO LLC
By:	/s/ P.K.M. Beall
Name: P.K.M. Beall
Title: President

[Signature Page to Voting Agreement]

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UNITHOLDER
TORTOISE CAPITAL ADVISORS, L.L.C., as investment adviser
By:	/s/ Matthew G.P. Sallee
Name: Matthew G.P. Sallee
Title: Managing Director

[Signature Page to Voting Agreement]

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Schedule A

Name of Unitholder; Address	Number of Common Units
Tortoise Capital Advisors, L.L.C. 11550 Ash Street, Suite 300 Leawood, KS 66211	11,499,731

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