FINDLAY, Ohio, and DENVER, Colorado Dec. 18, 2015 - MPLX LP (NYSE: MPLX) and MarkWest Energy Partners, L.P. (MarkWest) today announced the final results of the previously announced exchange offers (the 'Exchange Offers') for any and all of the $4.1 billion in aggregate principal amount of outstanding senior notes issued by MarkWest and MarkWest Energy Finance Corporation (the 'Existing MarkWest Notes') for (1) new senior notes issued by MPLX (the 'New MPLX Notes') and (2) cash, and related consent solicitations (the 'Consent Solicitations') to adopt certain amendments to the indentures governing the Existing MarkWest Notes.

The Exchange Offers and Consent Solicitations expired at 12:01 a.m., New York City time, on Dec. 18, 2015 (the 'Expiration Date'). As of the Expiration Date, the following principal amounts of each series of Existing MarkWest Notes were validly tendered and not validly withdrawn (and consents thereby validly given and not validly revoked):

The Exchange Offers and Consent Solicitations were made in connection with MPLX's acquisition of MarkWest, which was completed on Dec. 4, 2015, and pursuant to the terms and conditions set forth in the Offering Memorandum and Consent Solicitation Statement, dated Nov. 19, 2015 (the 'Offering Memorandum and Consent Solicitation Statement'), and related Letter of Transmittal.

Upon settlement of the Exchange Offers and Consent Solicitations, which is expected to occur on Tuesday, Dec. 22, 2015, MPLX will (i) issue to the holders of the Existing MarkWest Notes whose securities have been accepted for exchange New MPLX Notes in an equal principal amount to the principal amount of the Existing MarkWest Notes that have been accepted for exchange and (ii) pay to the holders of the Existing MarkWest Notes whose securities have been accepted for exchange a total of $4,036,374 in cash as part of the exchange consideration.

In addition, as previously disclosed, MarkWest received consents in the Consent Solicitations sufficient to approve amendments to the respective indentures governing the Existing MarkWest Notes. As a result, MarkWest and the trustee for the Existing MarkWest Notes entered into a supplemental indenture implementing those amendments to the indentures governing the Existing MarkWest Notes.

The New MPLX Notes will only be issued to eligible holders of Existing MarkWest Notes who have completed and returned an eligibility form confirming that they are either a 'qualified institutional buyer' under Rule 144A or not a 'U.S. person' and outside the United States under Regulation S for purposes of applicable securities laws.

The New MPLX Notes have not been and will not be registered under the Securities Act of 1933 or any state securities laws. Therefore, the New MPLX Notes may not be offered or sold in the United States absent registration or an applicable exemption from the registration requirements of the Securities Act of 1933 and any applicable state securities laws.

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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 network of common carrier crude oil and products pipeline assets located in the Midwest and Gulf Coast regions of the United States and a butane storage cavern located in West Virginia with approximately 1 million barrels of natural gas liquids storage capacity. In addition, MarkWest Energy Partners, L.P., a wholly owned subsidiary of MPLX, 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.

MPLX Investor Relations Contacts:
Geri Ewing (419) 421-2071
Teresa Homan (419) 421-2965
Joshua Hallenbeck (866) 858-0482

MPLX Media Contacts:
Chuck Rice (419) 421-2521
Brandon Daniels (419) 421-3127

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 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: 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; 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 MPLX's 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 Sept. 30, 2015, filed with the SEC. These risks, as well as other risks associated with MPLX, MWE and the 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 Oct. 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 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 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.

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