NEW YORK, Dec 30 (Reuters) - U.S. crude on the New York Mercantile Exchange futures on Friday ended 2011 up $7.45, or 8.2 percent, a third straight annual gain but off 2010's 15 percent jump, as export-disrupting civil war in Libya countered the effect of slowing economies and Europe's debt woes.

U.S. February crude fell 82 cents, or 0.82 percent, on the day to settle at $98.83 a barrel, ending the year on a weaker note.

Euro zone debt problems, slowing factories in China and rising U.S. oil inventories helped temper year-end sentiment even as potential threats to global supply in Iran, Iraq and Nigeria limited pressure on oil prices.

U.S. crude oil is expected to average $97 a barrel in 2012, up from the roughly $94.50 average for 2011, according to the most recent Reuters survey of analysts and consultants published on Dec. 21.

The Seaway pipeline is expected to begin carrying crude out of the oversupplied Midwest to U.S. Gulf Coast refineries by April, likely helping to narrow Brent oil's premium to the U.S. benchmark .

Iran's dispute with the West over Tehran's nuclear program, internal conflicts in neighboring Iraq and Syria, and fellow OPEC-member Nigeria are expected to keep potential supply disruptions as a supportive factor for oil prices in 2012.

Returning Libyan crude exports after its civil war, China's efforts to contain inflation and the potential impact of the euro zone's debt crisis were cited by experts as downside risks to oil demand and price increases.