NEW YORK, Dec 30 (Reuters) - Cotton ended 2011 as the worst-performing commodity market of the year, falling 36.6 percent from 2010 as record prices boosted output and decimated demand while a shaky global economy scared off investors.

Benchmark U.S. cotton futures closed at 91.80 cents per lb on Friday, up from 91.63 a day earlier but well off a record above $2.20 set in March.

Friday's settlement was down 36.6 percent from Dec. 31, 2010, when it settled at $1.4481 per lb. Last year, cotton was the second-best-performing market, rising more than 90 percent.

Open interest, an indicator of investor exposure, peaked at 223,405 lots on Feb. 9, data from ICE Futures U.S. showed.

Open interest dropped to a year low around 134,000 lots in July and stands at year-end near 150,000 lots, down more than 30 percent from the 2011 high, the ICE data showed.

Cotton enters 2012 with questions over fiber demand, especially after the U.S. Agriculture Department and influential industry publication Cotlook reduced their forecasts for world consumption in 2011/12.

Low cotton prices could result in reduced plantings, but if demand is weak, analysts believe values should still suffer.