Valero Energy ( VLO) erased 7.6% as the company's second-quarter profit missed analysts' estimates on higher-than-expected losses at its Canadian refinery. RPC Inc ( RES) and Talisman Energy ( TLM) erased 7.5% and 7.1%, respectively. Advantage Oil & Gas ( AAV) shed 6.7%. Suntech Power Holdings ( STP) declined 6.7% as Deutsche Bank equity analyst Eric Cheng has downgraded the stock to hold from buy with a price target of $6.2 per share. Newfield Exploration ( NFX) and Cheniere Energy Partners ( CQP) trimmed 6.6% and 6.5%, respectively. Rosetta Resources ( ROSE) lost 6.3% after receiving a downgrade to neutral from positive with a price target of $60 per share from Susquehanna equity analyst Gray Peckham. Also on the downside were Denbury Resources ( DNR) and Suncor Energy ( SU), closing the week down around 6%.