Oil prices fell on Thursday, after rising to five-month highs earlier this week on OPEC-led production cuts and free-falling Venezuelan output.
U.S. West Texas Intermediate crude oil futures settled $1.03 lower on Thursday, falling 1.6% to $63.58 per barrel. Earlier this week, WTI hit $64.79, its highest level since Nov. 1.
International benchmark Brent futures fell 90 cents, or 1.3%, at $70.83 a barrel. Brent hit a high going back to Nov. 12 at $71.78 on Wednesday.
Selling accelerated Thursday morning as U.S. crude dropped below $63.71 a barrel, a technically-significant level at which some funds had stops in place, triggering automatic sales, said Bob Yawger, director of energy futures at Mizuho in New York.
U.S. crude inventories surged by 7 million barrels to a 17-month high of 456.6 million barrels last week, the Energy Information Administration said on Wednesday. However, U.S. gasoline stocks fell by a whopping 7.7 million barrels, sending U.S. gasoline futures higher by 3.5 percent on their close on Wednesday.
U.S. crude oil production remained at a record 12.2 million bpd, making the United States the world's biggest oil producer ahead of Russia and Saudi Arabia.
The surging production and regional refinery outages have depressed prices of cash grades, putting more pressure on U.S. crude, said Yawger.
U.S. West Texas Intermediate crude at Midland on Thursday traded at the biggest discount to futures in almost four months after Phillips 66 closed a unit for maintenance at its Borger, Texas refinery, adding to a backlog of barrels as production climbs.
Oil markets are tightening amid the increasing effectiveness of U.S. sanctions on Iran and Venezuela, the International Energy Agency said on Thursday.
U.S. sanctions and power outages pushed OPEC member Venezuela's crude output to a long-term low of 870,000 bpd, IEA says. On Wednesday, OPEC reported Venezuela's March output sank to 732,000 bpd, citing independent sources, while figures provided by the country put production at 960,000 bpd.
Iranian supply could fall further after May if, as many expect, Washington tightens its sanctions against Tehran.
OPEC and its allies led by Russia are due to meet in Vienna on June 25-26 to set their policy.
Overall output from OPEC, which has agreed with allies to withhold 1.2 million bpd of crude from the market since the start of 2019, fell 550,000 bpd in March to 30.1 million bpd, the IEA said. OPEC's official report on Wednesday put the group's output at a four-year just over 30 million bpd.
OPEC may raise oil output from July if Venezuelan and Iranian supply drops further and prices keep rallying, because extending production cuts with Russia and other allies could overtighten the market, sources familiar with the matter said.
"Now there is a suggestion that OPEC may surprise us and raise production pre-emptively if we get a price spike," said Phil Flynn, an analyst at Price Futures Group in Chicago.
IEA, which coordinates the energy policies of developed nations, saw oil stocks in industrialized countries fall in February by 21.7 million barrels, putting inventories 16 million barrels above their five-year average.
Oil markets will remain tight "as long as Saudi Arabia continues to back the production cut deal as aggressively as it has done so far", said Ole Hansen, head of commodity strategy at Saxo Bank.
— CNBC's Tom DiChristopher contributed to this report.