MarkWest Energy Partners, L.P. (MarkWest) (NYSE: MWE) announced today that it has signed a 10-year agreement to become a firm shipper on the Mariner East pipeline subject to final regulatory approvals. Mariner East is currently designed to transport ethane and propane sourced at MarkWest’s Houston, Pennsylvania processing and fractionation complex to Sunoco’s Marcus Hook facility located near Philadelphia. Once delivered, the ethane-propane mix will be re-fractionated into purity products for sale into domestic and international markets. MarkWest has partnered with Sunoco Logistics Partners L.P. (Sunoco Logistics) (NYSE:SXL) through the development of Mariner West and Mariner East to deliver comprehensive solutions for its producer customers to market ethane and propane produced in the northeast to both domestic and international end-user markets. As a precursor to the announcement of a binding open season for the Mariner East Project, MarkWest began delivering propane from its Houston, Pennsylvania processing and fractionation complex to the Marcus Hook export facility for sale to international markets. “We are pleased to expand our partnership with Sunoco Logistics and commit capacity on Mariner East. The delivery of ethane and propane from the northeast US to both domestic and international markets is a critical step in ensuring that the Marcellus and Utica natural gas liquids markets remain in balance,” stated Frank Semple, Chairman, President and Chief Executive Officer of MarkWest. “Mariner East’s ability to further expand export capacity from Marcus Hook is an important milestone. MarkWest’s agreement to take capacity emphasizes our ongoing commitment to provide multiple marketing options that will continue to maximize the value of our producer customers’ natural gas liquids for years to come.” 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.