Denver-based MarkWest Energy Partners LP (NYSE: MWE) and its subsidiary MarkWest Energy Finance Corp. have priced at par an offering of $500 million in aggregate principal amount of 6.75% senior unsecured notes due 2020.

A portion of the net proceeds will be used to purchase any and all of the outstanding $225 million aggregate principal amount of its 6.875% senior notes due 2014, and $150 million aggregate principal amount of its 6.875% senior notes due 2014. Remaining net proceeds will be used to pay borrowings outstanding under its revolving credit facility, and to provide working capital for general partnership purposes.

Wells Fargo Securities, BofA Merrill Lynch, Barclays Capital, Morgan Stanley and RBC Capital Markets are joint book-running managers.

MarkWest Energy is midstream MLP focused on energy infrastructure in the southwest, Gulf Coast and Appalachian region including the Marcellus.