News Release

DENVER--(BUSINESS WIRE)--Oct. 31, 2012-- MarkWest Energy Partners (NYSE: MWE) (MarkWest) and Antero Resources (Antero) announced today that MarkWest recently commenced operation of its Sherwood I processing facility and the initial phase of its high pressure gas gathering system located in Harrison and Doddridge Counties of West Virginia. The 200 million cubic feet per day (MMcf/d) Sherwood I facility is the first phase of its planned processing facilities at the Sherwood complex. MarkWest is currently constructing the 200 MMcf/d Sherwood II processing facility which is expected to be in service during the second quarter of 2013. MarkWest and Antero have entered into agreements for the potential development of a third processing facility at the same site, Sherwood III, to support additional rich gas production. If installed, the third facility would bring total processing capacity of the Sherwood complex to 600 MMcf/d. Sherwood is located near the center of Antero’s rapidly-growing, rich gas production in northern West Virginia and the complex’s associated volumes will be gathered by MarkWest, Antero, and other providers. MarkWest and Antero estimate that future capacity at the Sherwood complex could exceed 1 billion cubic feet per day (Bcf/d) with the continued development by Antero of its rich gas acreage in the area.

Antero has over 200,000 net acres of leasehold in northern West Virginia that holds rich gas reserves. Antero is currently flowing approximately 90 MMcf/d through the Sherwood I processing plant from a portion of its 104 horizontal Marcellus wells that are producing over 400 MMcf/d of gross operated production in West Virginia. Antero plans to significantly increase Sherwood I throughput over the next several months.

Antero will have access to the full suite of MarkWest’s midstream services in the Marcellus Shale and all of the announced ethane and propane pipeline projects. Natural gas liquids (NGLs) recovered at the Sherwood complex will be delivered via MarkWest’s NGL pipeline network that also connects MarkWest’s Mobley and Majorsville complexes to its Houston fractionation and marketing complex. Pending the completion of MarkWest’s previously announced fractionation projects, including the 100,000 barrels per day (Bbl/d) fractionation complex that is being developed in Harrison County Ohio with its partner, The Energy and Minerals Group, MarkWest’s total announced NGL fractionation capacity serving the Marcellus and Utica Shales will be approximately 275,000 Bbl/d. This fractionation capacity includes nearly 155,000 Bbl/d of purity ethane facilities and 120,000 Bbl/d of propane and heavier NGL fractionation. Antero’s NGLs produced at Sherwood will also benefit from MarkWest’s extensive marketing operations, which include truck, rail, and pipeline logistics; storage, and wholesale distribution.

The development of the hydrocarbon-rich area of northern West Virginia is critical to the growth of MarkWest’s Liberty segment and the expansion of its processing complexes in the Marcellus Shale. By the end of 2014, MarkWest will have over 2.5 Bcf/d of processing capacity in Pennsylvania and West Virginia and the ability to continue offering its Marcellus producer customers like Antero premier midstream solutions. The natural gas production and associated NGL production in MarkWest’s Liberty segment are supported by largely fee-based, long-term agreements.

“Antero is a proven and highly successful operator in unconventional resource plays and we are very pleased to support their growth in the Marcellus Shale,” said Frank Semple, Chairman, President and Chief Executive Officer of MarkWest. “The commencement of operations at our Sherwood complex underscores our ongoing commitment to lead the development of solutions in the liquids-rich areas of the Marcellus and Utica Shales.”

“The start-up of Sherwood I is an exciting event for Antero as it represents the first step in realizing the value of our large Marcellus rich gas resource base in West Virginia,” said Paul Rady, Chairman and Chief Executive Officer of Antero. “We have enjoyed a long relationship with Frank Semple and his team dating back to the Woodford Shale Play, so we have a lot of confidence in partnering with MarkWest to bring rich gas processing and marketing capability to the Marcellus in West Virginia.”

About MarkWest Energy Partners, L.P.

MarkWest Energy Partners, L.P. is a master limited partnership engaged in the gathering, transportation, and processing of natural gas; the transportation, fractionation, marketing, and storage of natural gas liquids; and the gathering and transportation of crude oil. MarkWest has extensive natural gas gathering, processing, and transmission operations in the southwest, Gulf Coast, and northeast regions of the United States, including the Marcellus Shale, and is the largest natural gas processor and fractionator in the Appalachian region.

This press release includes “forward-looking statements.” All statements other than statements of historical facts included or incorporated herein may constitute forward-looking statements. Actual results could vary significantly from those expressed or implied in such statements and are subject to a number of risks and uncertainties. Although MarkWest believes that the expectations reflected in the forward-looking statements are reasonable, MarkWest can give no assurance that such expectations will prove to be correct. The forward-looking statements involve risks and uncertainties that affect operations, financial performance, and other factors as discussed in filings with the Securities and Exchange Commission. Among the factors that could cause results to differ materially are those risks discussed in the periodic reports filed with the SEC, including MarkWest’s Annual Report on Form 10-K for the year ended December 31, 2011 and its Quarterly Reports on Form 10-Q for the quarters ended March 31, 2012 and June 30, 2012. You are urged to carefully review and consider the cautionary statements and other disclosures made in those filings, specifically those under the heading “Risk Factors.” MarkWest does not undertake any duty to update any forward-looking statement except as required by law.

About Antero Resources

Antero Resources is an independent oil and natural gas company engaged in the acquisition, development and production of unconventional oil and liquids-rich natural gas properties primarily located in the Appalachian Basin in West Virginia, Ohio and Pennsylvania, and in the Piceance Basin in Colorado. Our website is located at www.anteroresources.com.

This release includes “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Such forward-looking statements are subject to a number of risks and uncertainties, many of which are beyond Antero’s control. All statements, other than historical facts included in this release, are forward-looking statements. All forward-looking statements speak only as of the date of this release. Although Antero believes that the plans, intentions and expectations reflected in or suggested by the forward-looking statements are reasonable, there is no assurance that these plans, intentions or expectations will be achieved. Therefore, actual outcomes and results could materially differ from what is expressed, implied or forecast in such statements.

We caution you that these forward-looking statements are subject to all of the risks and uncertainties, most of which are difficult to predict and many of which are beyond our control, incident to the exploration for and development, production, gathering and sale of natural gas and oil. These risks include, but are not limited to, commodity price volatility, inflation, lack of availability of drilling and production equipment and services, environmental risks, drilling and other operating risks, regulatory changes, the uncertainty inherent in estimating natural gas and oil reserves and in projecting future rates of production, cash flow and access to capital, the timing of development expenditures, and the other risks described under the heading “Item 1A. Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2011.

Photos/Multimedia Gallery Available: http://www.businesswire.com/cgi-bin/mmg.cgi?eid=50460212&lang=en

Source: MarkWest Energy Partners, L.P.

MarkWest Energy Partners, L.P.
Frank Semple, 866-858-0482
Chairman, President & CEO
or
Nancy Buese, 866-858-0482
Senior VP & CFO
or
Josh Hallenbeck, 866-858-0482
VP of Finance & Treasurer
investorrelations@markwest.com
or
Antero Resources
Chad Green, 303-357-7339
Finance Director
cgreen@anteroresources.com