Supply from the 11 members of the Organization of the Petroleum Exporting Countries with output targets, all except Iraq, has averaged 26.70 million barrels per day (bpd) this month, down from 26.79 million bpd in October, according to the survey of oil companies, OPEC officials and analysts. The decrease reflects reductions from Nigeria, Venezuela, Saudi Arabia, the United Arab Emirates, Qatar and Angola.

OPEC has limited its production over the last two years in an attempt to stabilize prices. On Oct. 14, the organization left its output targets unchanged, maintaining a deal agreed in December 2008 when it imposed a record supply cut of 4.2 million bpd.

Many OPEC members have been informally boosting supply since 2009 as prices and demand have recovered.

Crude oil has mostly traded between $70 and $80 per barrel over the last year, a level most OPEC members find comfortable, and was well above that level in early European trade on Monday at around $84.50.

The survey found that the 11 members bound by the OPEC output agreement met 56 percent of their promised supply reduction in November, up 2 percentage points from October.

Total OPEC supply including Iraq was down 70,000 bpd, according to the survey.

"OPEC production is essentially stable with slightly better compliance with output targets," said Christophe Barret, global oil analyst at Credit Agricole. "The small reduction in output is due mainly to supply disruptions."

Nigerian supply has fallen by 40,000 bpd on average over the month, mainly because of a leak on the Trans-Niger pipeline that trade sources said was caused by thieves who siphoned off oil for resale. The incident curbed output of Bonny Light crude, one of Nigeria's most popular oil production streams.

Industry sources said two Bonny cargoes were delayed into December from November because of the drop in output.

Shell, operator of the Bonny stream, has said it was ramping up production after fixing the pipeline, pointing to an earlier end to the disruption than some traders had expected.

Angolan output has also declined in November, falling by about 30,000 bpd. Grades including Cabinda and Girassol have loaded fewer barrels, according to loading programs, with trade sources saying technical problems and maintenance at some oil fields have produced some unexpected delays.