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Oil retreated from a 16-month high after OPEC pumped a record amount of crude in November.

Futures slid as much as 2.9 percent in New York after rising 15 percent over the previous four sessions. OPEC boosted production to 34.16 million barrels a day last month, according to a Bloomberg News survey, with Angola, Libya and Nigeria leading the gains.

Attention is shifting to which non-OPEC producers will join Russia in reducing output when they meet in Vienna on Saturday. OPEC is hoping they will cut 300,000 barrels a day further than the 300,000 already promised by Russia.

Oil topped $50 a barrel after the Organization of Petroleum Exporting Countries agreed Wednesday to trim the group's output by 1.2 million barrels a day from January to stem a supply glut and buoy prices. Russia — which isn't part of the bloc — has also pledged a reduction of as much as 300,000 barrels.

"There are two things moving us lower, the first being the rise in OPEC production," said Bob Yawger, director of the futures division at Mizuho Securities USA Inc. in New York. "There's also skepticism about the meeting next weekend. They are going to be hard pressed to squeeze 300,000 barrels from this crew."

West Texas Intermediate for January delivery dropped $1.14, or 2.2 percent, to $50.65 a barrel at 10:54 a.m. on the New York Mercantile Exchange. The contract rose 0.2 percent to $51.79 on Monday, the highest close since July 2015. Total volume traded was about 28 percent above the 100-day average.

The discount between WTI futures closest to delivery and those for delivery in coming months widened to the highest since April Tuesday, even as some sections of the curve enter backwardation. A growing discount for front-month futures, known as contango, typically signals ample stockpiles.

"Contango in the front months widened, which is a cautionary signal for the market," Yawger said.

Brent for February settlement fell 91 cents, or 1.7 percent, to $54.03 a barrel on the London-based ICE Futures Europe exchange. Futures climbed 0.9 percent to $54.94 on Monday, also the highest close since July 2015. The global benchmark crude traded at a $2.13 premium to February WTI.

"No trend has been interrupted," Thomas Finlon, director of Energy Analytics Group LLC in Wellington, Florida, said by telephone. "The market is clearly in an upward trend. This is probably just a pause before the upcoming OPEC, non-OPEC meeting."

OPEC has invited Russia, Mexico, Kazakhstan, Oman, Bahrain, Colombia, Congo, Egypt, Trinidad and Tobago, Turkmenistan, Azerbaijan, Uzbekistan, Bolivia and Brunei to the talks. Together, the 14 nations pumped about 18.8 million barrels a day of oil last year, equivalent to 20 percent of global supply, according to data from BP.

Russia's Energy Minister Alexander Novak will meet oil companies Wednesday ahead of talks with OPEC representatives on Dec. 10, according to people with knowledge of the matter.

"We will see $60 by the end of the month and $70 next year," Pierre Andurand, chief investment officer and founder of Andurand Capital Management, said in an interview on Bloomberg television. "We are still at very low prices."

Andurand, who correctly called the top of the oil market in 2008, has been bullish this year. The founder and chief investment officer of Andurand Capital Management said $100 oil is possible again by the end of the decade.

Other oil-market news:

• U.S. crude inventories probably dropped by 1.5 million barrels last week, according to the median estimate in a Bloomberg survey before EIA data.

• Saudi Arabia cut pricing for January oil sales to Asia, according to an emailed statement from state-owned Saudi Arabian Oil Co.