NEW YORK, Sept. 12 (Xinhua) -- U.S. crude oil price ended higher on Monday after choppy trading amid European debt concerns and global economic worries.

Crude prices swang on Monday, with U.S. crude benchmark dipping to the low of 85 dollars a barrel, as concerns about European debt crisis and global economic slowdown lingered.

Fears of Greece's default were mounting as German parties started to discuss about it in public. Analysts said it would be only a matter of time for Greece's default.

Over the weekend, the G7 finance ministers pledged to coordinate in addressing the economic slowdown, but offered no concrete steps.

Because of a worsening economic outlook, the Organization of the Petroleum Exporting Countries (OPEC) slashed its forecast for global oil demand growth in 2011 and 2012. OPEC said in a report that global oil demand would rise 1.06 million barrels per day in 2011, 150,000 lower than last estimate. And its new forecast for 2012 was 40,000 fewer than last estimate.

OPEC said that a sluggish U.S. economy could further weigh on oil demand.

In the Gulf of Mexico, concerns about production shut caused by bad weather were eased after Tropical Storm Nate made a landfall elsewhere and no further storms were expected in the short term.

In Libya, oil firm Arabian Gulf Oil Co. said on Monday it started to restore production at the eastern oil field, which sent signals that Libya's oil supplies would gradually come back to markets after 6-month absence.

Light, sweet crude for October delivery climbed 95 cents, or 1. 09 percent to settle at 88.19 dollars a barrel on the New York Mercantile Exchange, after trading from 85.00 dollars to 88.95 dollars a barrel. But in London, Brent crude for October delivery fell 52 cents, or 0.46 percent to close at 112.25 dollars a barrel.