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.