MarkWest Energy Partners, L.P. (NYSE: MWE) (“MarkWest” or “the Partnership”) announced today the commencement of Bluestone II, a 120 million cubic feet per day (MMcf/d) cryogenic processing facility. The Bluestone II plant is part of the Partnership’s Keystone assets in Butler County, Pennsylvania and increases processing capacity for Marcellus producers operating in the rich-gas area of northwest Pennsylvania to 210 MMcf/d. Concurrently with the new processing plant, MarkWest has also completed 20,000 barrels per day of ethane and heavier fractionation capacity at the Bluestone facility, and a 32 mile purity ethane pipeline connecting to Mariner West. The Bluestone II plant primarily supports the expanding rich-gas production of Rex Energy Corporation (NASDAQ: REXX) (“Rex Energy”). Rex Energy now has 190 MMcf/d of dedicated processing capacity at MarkWest’s Keystone facilities, which also consist of 50 MMcf/d of capacity at the Bluestone I plant and 40 MMcf/d of capacity at the Sarsen facility. MarkWest continues to develop its rich-gas gathering system throughout Butler County and surrounding areas in order to support the continued growth of its processing facilities. “We are excited to expand our processing and fractionation capacity in the Marcellus Shale with the addition of new facilities in Butler County,” stated Frank Semple, Chairman, President, and Chief Executive Officer of MarkWest. “Rex is a proven operator and has been highly successful developing their Marcellus and Upper Devonian resources in northwest Pennsylvania.” MarkWest Energy Partners, L.P. is a master limited partnership engaged in the gathering, processing and transportation of natural gas; the gathering, transportation, fractionation, storage and marketing of natural gas liquids; and the gathering and transportation of crude oil. MarkWest has a leading presence in many unconventional gas plays including the Marcellus Shale, Utica Shale, Huron/Berea Shale, Haynesville Shale, Woodford Shale and Granite Wash formation. 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 (SEC). 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, 2013. 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.