MarkWest Energy Partners, L.P. (MarkWest) (NYSE: MWE) today announced the execution of two major agreements related to its ongoing development of the hydrocarbon-rich area of the Marcellus shale. The first agreement is a long-term fee-based arrangement with affiliates of Chesapeake Energy Corporation (NYSE:CHK) to expand its Marcellus gas processing capacity to support Chesapeake’s rapidly growing rich natural gas production in an approximately 185 square mile dedication area, which includes portions of Brooke, Ohio, and Marshall Counties in northern West Virginia and Washington County in southwestern Pennsylvania. The second agreement is a long-term fee-based arrangement with Antero Resources Appalachian Corporation (Antero Resources) to install significant gathering facilities in support of Antero’s rapidly growing rich natural gas production in Doddridge and Harrison Counties in northern West Virginia. In support of the agreement announced today with Chesapeake, MarkWest will expand the gas processing capacity at its Majorsville, West Virginia processing complex by 400 million cubic feet per day (MMcf/d) from 670 MMcf/d to approximately 1.1 billion cubic feet per day (Bcf/d). This expansion capacity is being provided in exchange for the significant dedication of acreage made by Chesapeake to the Majorsville processing complex. MarkWest will construct two new 200 MMcf/d cryogenic gas plants that are expected to be completed in late 2013 and mid 2014. The gathering facility expansion to support Antero Resources will expand MarkWest’s existing gathering operations in southwestern Pennsylvania into a key part of West Virginia and includes the installation of two large high-pressure gathering headers and associated compressor stations in Doddridge and Harrison Counties, West Virginia. The new gathering system will have the capacity to initially deliver more than 300 MMcf/d of Antero’s rich gas to MarkWest’s Sherwood gas processing complex. The first phase of the gathering system will be completed in the third quarter of 2012 in conjunction with the completion of the 200 MMcf/d Sherwood I processing facility. MarkWest previously announced the expansion of the Sherwood processing complex to include the construction of the 200 MMcf/d Sherwood II processing facility, which is expected to come online in the second quarter of 2013 and will increase the total capacity of the Sherwood gas processing complex to 400 MMcf/d.