MarkWest Energy Partners Announces Release Date for Third Quarter 2015 Financial Results

MarkWest Energy Partners, L.P. (NYSE: MWE) will announce third quarter 2015 financial results before market open on Wednesday, November 4, 2015, and will host a conference call to discuss the results at 12:00 p.m. ET on the same day.

The conference call can be accessed by dialing (800) 475-0218 (passcode “MarkWest”) or via webcast by accessing the “Presentations & Webcasts” link located under the Investor Relations section of the MarkWest website at www.markwest.com.

A replay of the conference call will be accessible on the MarkWest website or by dialing (800) 839-5571 (no passcode required).

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MarkWest Energy Partners, L.P. is a master limited partnership that owns and operates midstream services related 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 where it provides midstream services to its producer customers.

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 Securities and Exchange Commission (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 Reports on Form 10-Q for the quarter ended June 30, 2015. These risks, as well as other risks associated with the Partnership, MPLX and the proposed transaction are also more fully discussed in the preliminary joint proxy statement and prospectus included in the registration statement on Form S-4 filed with the Securities and Exchange Commission (the “SEC”) by MPLX on October 8, 2015. 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 does 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 that includes a preliminary joint proxy statement and a prospectus. The Partnership and MPLX expect to file amendments to these filings before they become effective. Investors and security holders are urged to read all relevant documents filed with the SEC, including the preliminary joint proxy statement and prospectus and any further amendments thereto when they become available, because they will contain important information about the proposed transaction. Investors and security holders are able to obtain the documents and any further amendments (once available) 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 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, and in the preliminary joint proxy statement filed by MPLX with the SEC on October 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 preliminary joint proxy statement filed by MPLX with the SEC on October 8, 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 preliminary joint proxy statement and prospectus regarding the acquisition. These documents and any further amendments (when available) may be obtained free of charge from the SEC’s website http://www.sec.gov, or from the Partnership 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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