X0304 4 2012-01-17 0 0001166036 MARKWEST ENERGY PARTNERS L P MWE 0001526751 Rosson Paula L 1515 ARAPAHOE STREET TOWER 1 SUITE 1600 DENVER CO 80202 0 1 0 0 VP/Chief Accounting Officer Common Units 2012-01-17 4 S 0 450 56.34 D 21271 D Sales were effected pursuant to instructions given by the reporting person on March 7, 2011, pursuant to a Rule 10b5-1 trading plan. Amount of securities beneficially owned following the reported transaction(s) includes Common Units owned and Restricted Units subject to varying vesting terms. /s/ Sean M McKendry as POA for Paula L Rosson 2012-01-17