NEW YORK (TheStreet) -- Tesoro (TSO), National Oilwell Varco (NOV - Get Report) and Dresser-Rand Group (DRC) showed strength this past week, while InterOil (IOC), Lufkin Industries (LUFK) and Exterran Holdings (EXH) saw substantial declines.

Tesoro led the pack of energy winners last week by gaining 16.2%.

National-Oilwell Varco rose 14.8% after Standpoint Research initiated coverage on the stock with a buy rating and a price target of $74, which is 26% greater than current levels.

Dresser-Rand Group increased 12.1% after Tupi and Guara awarded the company a compression equipment and services contract valued nearly $700 million. The deal includes up to 80 Datum compressor trains that will be installed on eight floating, production, storage and offloading (FPSO) vessels.

Valero Energy ( VLO - Get Report) improved 11.2%. Last week, the company completed the purchase of Murphy Oil's ( MUR) refinery and related logistics assets at Meraux for $325 million along with crude oil inventories valued $260 million.

Yingli Green Energy Holdings ( YGE) was up 10.6% after research analysts at Bank of America/Merrill Lynch initiated coverage on the stock with a buy rating.

Eni SpA ( E) increased 9.5%. The company announced last week it has reached an agreement with French power group GDF Suez to acquire a 10.4% stake in Elgin-Franklin gas condensate fields for $804.5 million.

Halliburton ( HAL) appreciated 9.2%. The company has completed the acquisition of Multi-Chem Group announced initially in September.

Solar companies ReneSola ( SOL) and LDK Solar ( LDK) gained 9.9% and 9%, respectively, while JA Solar Holdings ( JASO) rose 5.6%.

Noble Energy ( NBL) added 6.3% at the close last week. The company has finalized its joint venture partnership with Consol Energy ( CNX) for the development of Marcellus Shale assets in Southwest Pennsylvania and Northwest West Virginia, the U.S.

InterOil shed 12.8%, emerging the top loser this past week.

Lufkin Industries fell 11.4%. Last week, the company reported preliminary unaudited financial results for the third quarter of 2011. Based on the financial data, the company expects to report third-quarter revenue in the range of $225 million to $235 million, vs. the previous guidance of $230 million to $250 million, and earnings per diluted share between 55 cents and 60 cents, compared with the earlier view of $0.72 to $0.82.

Exterran Holdings dropped 9.6% last week.

Frontline ( FRO) fell 9.3%. Dahlman Rose has downgraded the stock to sell from the earlier hold rating with a price target of $3.50, representing 20.5% downside from current levels.

EXCO Resources ( XCO) fell 6.4% at close last week. The company said it will not develop its Mt. Colin copper and gold deposit in Queensland and is considering selling the property.

First Solar ( FSLR) declined 5.5% after Stifel Nicolaus lowered the stock's price target to $107.00 from the previous target of $168.00.

Swift Energy ( SFY) declined 4.9% after research analysts at SunTrust downgraded the stock to neutral from buy.