Exhibit 99.1

MarkWest Energy Partners Reports Third Quarter 2015 Financial Results

·                  Reported DCF of $176.0 million and Adjusted EBITDA of $230.3 million for the third quarter 2015

·                  Increased quarterly distribution to 93 cents per common unit with a 96 percent distribution coverage

·                  Received the first place ranking for Total Customer Satisfaction and five other categories in EnergyPoint Research’s 2015 Oil & Gas Midstream Services Customer Satisfaction Survey

·                  Reported record total gas volumes of 5.8 Bcf/d for the third quarter 2015, an increase of 28 percent from the third quarter 2014

·                  Processing capacity utilization averaged approximately 75 percent during the third quarter 2015, while the Partnership’s total processing capacity increased by almost 18% since June 2015

·                  Commenced operations of the 80 MMcf/d expansion of Carthage IV plant, increasing total processing capacity in East Texas to 600 MMcf/d

·                  Announced long-term fee-based agreement with Ascent Resources to support their Utica dry gas development

·                  Announced long-term fee-based agreement with Newfield Exploration to gather crude oil in the Cana-Woodford Shale

DENVER—November 4, 2015—MarkWest Energy Partners, L.P. (NYSE: MWE) (“the Partnership”) today reported quarterly cash available for distribution to common unitholders, or distributable cash flow (DCF), of $176.0 million for the three months ended September 30, 2015, and $522.1 million for the nine months ended September 30, 2015. DCF for the three months ended September 30, 2015 represents distribution coverage of 96 percent. The third quarter 2015 distribution of $184.1 million, or $0.93 per common unit, will be paid to unitholders on November 13, 2015. The third quarter 2015 distribution represents an increase of $0.01 per common unit or 1.1 percent over the second quarter 2015 distribution and an increase of $0.04 per common unit or 4.5 percent compared to the third quarter 2014 distribution. As a Master Limited Partnership, cash distributions to common unitholders are largely determined based on DCF. A reconciliation of DCF to net income, the most directly comparable GAAP financial measure, is provided within the financial tables of this press release.

The Partnership reported Adjusted EBITDA for the three and nine months ended September 30, 2015 of $230.3 million and $678.8 million, respectively, compared to $235.5 million and $631.3 million for the respective three and nine months ended September 30, 2014. The Partnership believes the presentation of Adjusted EBITDA provides useful information because it is commonly used by investors in Master Limited Partnerships to assess financial performance and operating

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results of ongoing business operations. A reconciliation of Adjusted EBITDA to net income, the most directly comparable GAAP financial measure, is provided within the financial tables of this press release.

The Partnership reported income (loss) before provision for income tax for the three and nine months ended September 30, 2015 of $51.4 million and ($45.0) million, respectively. Income before provision for income tax includes (a) non-cash gains (losses) associated with the change in fair value of derivative instruments of $12.2 million and ($3.4) million for the respective three and nine months ended September 30, 2015, (b) non-cash impairments associated with our Southwest segment of $25.5 million for the nine months ended September 30, 2015, and (c) loss on redemption of debt of $117.9 million for the nine months ended September 30, 2015. Excluding these items, income before provision for income tax for the three and nine months ended September 30, 2015 would have been $39.2 million and $101.8 million, respectively.

“Our solid third-quarter results reflect the resiliency of our business model during this period of extremely low commodity prices.  We will continue to optimize our capital and efficiently execute our plan in order to support our producer customers and growing volumes in many of the nation’s most economic resource plays. Our focus on operational excellence and customer service has once again resulted in MarkWest achieving the number one ranking in the industry-wide EnergyPoint Customer Satisfaction annual survey,” stated Frank Semple, Chairman, President and Chief Executive Officer of MarkWest. “We also look forward to the successful completion of our strategic combination with MPLX, which will create an incredibly powerful midstream company with an unrivaled growth profile.  This merger will create one of the largest MLPs in the industry with the unique combination of MarkWest’s best-of-class organic growth and MPLX’s long-term inventory of drop down EBITDA from Marathon Petroleum Corporation.  The combined company with the strong parental support and the investment grade balance sheet will support an ongoing inventory of high-quality, fee-based midstream projects and long-term mid-twenty percent distribution growth.”

BUSINESS HIGHLIGHTS

MarkWest/MPLX Merger:

·                  On July 11, 2015, the Partnership entered into a definitive merger agreement, whereby it would become a wholly owned subsidiary of MPLX LP (NYSE: MPLX). The Partnership’s common unitholders would receive 1.09 MPLX common units per Partnership common unit, and their pro rata share of a one-time cash payment of $675 million based on the total number of common units and Class B units outstanding at closing, which equates to approximately $3.27 per unit based on the current unit count. The transaction has received regulatory approval and is subject to approval by the Partnership’s unitholders.  The Partnership declared a record date of October 5, 2015 and has scheduled a special meeting of common unitholders to be held on Tuesday, December 1, 2015, at 9:00 a.m. Mountain Standard Time.  The meeting will be held at the Partnership’s offices at 1515 Arapahoe Street, Tower 1, Suite 1600, Denver, Colorado 80202.  The Partnership urges unitholders to 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.

Marcellus:

·                  In July, the Partnership commenced operations of Sherwood VI, a 200 million cubic feet per day (MMcf/d) processing plant at the Sherwood complex in Doddridge County, West Virginia. The new plant is anchored by Antero Resources Corporation (NYSE: AR) and increases total processing capacity of the Sherwood complex to 1.2 billion cubic feet per day (Bcf/d). The

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Partnership also expects to place into service 40,000 barrels per day (Bbl/d) of de-ethanization capacity by the end of 2015, and is constructing a seventh 200 MMcf/d processing plant at the Sherwood complex with a scheduled completion in the first quarter 2017.

Utica:

·                  In August, the Partnership and The Energy & Minerals Group (EMG) announced the development of a new, large-scale dry gas gathering system to support Ascent Resources’ development program in the Utica Shale. Ascent Resources has dedicated approximately 100,000 gross acres in northern Belmont and Jefferson counties, Ohio. The system will be designed to gather more than 2 Bcf/d of gas, and could ultimately consist of more than 250 miles of pipeline and more than 200,000 horsepower of compression. Initial operation is expected to begin by the end of 2015.  Development of the new system will occur under a new joint venture, which will be owned two-thirds by the Partnership and one-third by EMG.

Southwest:

·                  In October, the Partnership increased total processing capacity of its Carthage IV plant in Panola County, Texas by 80 MMcf/d, and currently supports Anadarko Petroleum Corporation (NYSE: APC) and other producers operating in the Haynesville Shale and Cotton Valley formation with 600 MMcf/d of total capacity in East Texas.

·                  Today, the Partnership is announcing the execution of a long-term, fee-based agreement with Newfield Exploration Company (NYSE: NFX) to develop a crude oil gathering system in the Cana-Woodford Shale. The new system will be developed in conjunction with the rich-gas system already being constructed to support Newfield’s STACK acreage in Kingfisher, Blaine, and Canadian counties, Oklahoma.

Capital Markets:

·                  During the third quarter of 2015, the Partnership issued 3.8 million common units and received net proceeds of $198.3 million.  Fourth quarter to date we have received over $120 million of net proceeds.

FINANCIAL RESULTS

Balance Sheet:

·                  As of September 30, 2015, the Partnership had $629.7 million of remaining capacity under its $1.3 billion Senior Secured Credit Facility after consideration of $8.3 million of outstanding letters of credit and $662.0 million of outstanding borrowings.

Operating Results:

·                  Operating income before items not allocated to segments for the three months ended September 30, 2015, was $247.6 million, a decrease of $9.3 million when compared to $256.9 million over the same period in 2014. This decrease was primarily attributable to the decline in commodity pricing, partially offset by higher processing volumes. Processed volumes continued to increase in the third quarter of 2015, growing approximately 28 percent when compared to the third quarter of 2014, primarily due to the Partnership’s Marcellus and Utica segments.

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A reconciliation of operating income before items not allocated to segments to income before provision for income tax, the most directly comparable GAAP financial measure, is provided within the financial tables of this press release.

·                  Operating income before items not allocated to segments does not include gains (losses) on commodity derivative instruments. Realized gains (losses) on commodity derivative instruments were $11.8 million in the third quarter of 2015 and ($0.9) million in the third quarter of 2014.

Capital Expenditures:

·                  For the three months ended September 30, 2015, the Partnership’s portion of capital expenditures was $422.7 million.

2015 ADJUSTED EBITDA, DCF AND CAPITAL EXPENDITURE FORECAST

For 2015, the Partnership’s Adjusted EBITDA forecast remains in a range of $925 million to $975 million and DCF remains in a range of $700 million to $750 million based on its current forecast of operational volumes and prices for natural gas liquids, crude oil, natural gas, and derivative instruments currently outstanding.

The Partnership’s portion of growth capital expenditures for 2015 is expected to be approximately $1.6 billion. The Partnership’s forecasted maintenance capital for 2015 is approximately $20 million.

2016 ADJUSTED EBITDA, DCF AND CAPITAL EXPENDITURE FORECAST

For 2016, the Partnership forecasts Adjusted EBITDA in a range of $1.05 billion to $1.15 billion and DCF in a range of $800 million to $870 million based on its current forecast of operational volumes and prices for natural gas liquids, crude oil, natural gas, and derivative instruments currently outstanding.  A sensitivity analysis for forecasted 2016 DCF based on changes in composite NGL prices and changes in volume assumptions is provided within the tables of this press release.

The Partnership expects a 4.3% distribution growth rate in 2016 and also expects to be able to achieve an 8% to 10% annual distribution growth rate from 2017 to 2020 based on our analysis of producer customers’ development programs and forecasted commodity prices.

The Partnership’s portion of growth capital expenditures for 2016 is forecasted in a range of $900 million to $1.5 billion.  Maintenance capital for 2016 is forecasted at approximately $25 million.

CONFERENCE CALL

The Partnership will host a conference call and webcast on Wednesday, November 4, at 12:00 p.m. Eastern Time to review its third quarter 2015 financial results. Interested parties can participate in the call by dialing (800) 475-0218 (passcode “MarkWest”) approximately ten minutes prior to the scheduled start time. To access the webcast and associated third quarter 2015 earnings call presentation, please visit the Investor Relations section of the Partnership’s website at www.markwest.com. A replay of the conference call will be available on the Partnership’s 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.

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 Report on Form 10-Q for the quarter ended September 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 proxy statement and prospectus included in the registration statement on Form S-4 filed with the SEC by MPLX and declared effective by the SEC on October 29, 2015. The Partnership has mailed the proxy statement/prospectus to its unitholders. 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 definitive proxy statement and a prospectus and was declared effective by the SEC on October 29, 2015. Investors and security holders are urged to read all relevant documents filed with the SEC, including the definitive 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 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 prospectus filed by MPLX on October 30, 2015 and the related Registration Statement on Form S-4, which was declared effective by the SEC on October 29, 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 definitive proxy statement filed by the Partnership, 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 joint proxy

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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 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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MarkWest Energy Partners, L.P.

Financial Statistics

(unaudited, in thousands, except per unit data)

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MarkWest Energy Partners, L.P.

Operating Statistics (1)

(1)         Refer to Item 2 in Form 10-Q for additional disclosures.

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MarkWest Energy Partners, L.P.

Reconciliation of GAAP Financial Measure to Non-GAAP Financial Measure

Operating Income before Items not Allocated to Segments (1)

(unaudited, in thousands)

(1) Refer to footnote 15, Segment Information, in Form 10-Q for additional disclosures.

(2) Amounts represent revenues and expenses associated with the Northeast segment fractionation completed on behalf of the Marcellus segment.

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MarkWest Energy Partners, L.P.

Reconciliation of GAAP Financial Measure to Non-GAAP Financial Measure

Operating Income before Items not Allocated to Segments (1)

(unaudited, in thousands)

(1) Refer to footnote 15, Segment Information, in Form 10-Q for additional disclosures.

(2) Amounts represent revenues and expenses associated with the Northeast segment fractionation completed on behalf of the Marcellus segment.

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MarkWest Energy Partners, L.P.

Reconciliation of GAAP Financial Measure to Non-GAAP Financial Measure

Distributable Cash Flow

(unaudited, in thousands)