Oil slipped to $66 a barrel on Friday, under pressure from concerns that rising U.S. oil output and exports will offset OPEC-led attempts to erode stockpiles with output curbs.
U.S. oil production last week was 10.27 million barrels per day, a record level if confirmed by monthly figures. Crude exports jumped to more than 2 million bpd, close to a record high of 2.1 million hit in October.
"The U.S. is pumping out a record amount of oil," said Naeem Aslam, chief market analyst at Think Markets UK Ltd.
"The bull rally which we have seen for the black gold could fade away as the U.S. oil production undermines the OPEC production cut commitments," he said.
Brent crude, the global benchmark, was down 34 cents at $66.05 at 0934 GMT. Prices had rallied in early 2018 and reached $71.28 on Jan. 25, the highest since December 2014.
U.S. crude fell 27 cents to $62.50.
Oil also slipped as the U.S. dollar strengthened. A stronger dollar can make oil and other commodities denominated in the U.S. currency more expensive for other currency holders.
The latest decline for crude came despite the U.S. Energy Information Administration reporting on Wednesday that crude stocks fell unexpectedly by 1.6 million barrels. Analysts said low import figures contributed to the decline.
The Organization of the Petroleum Exporting Countries is not outwardly worried by rising in U.S. output and says it is comfortable at the speed the market is moving towards balance.
"I think the pace is excellent, the deal is working and we're very happy with it," United Arab Emirates Energy Minister Suhail al-Mazroui, the current OPEC president, told Reuters on Wednesday. "But the job is not yet complete."
In January 2017, OPEC and allies including Russia began to cut production by about 1.8 million bpd, almost 2 percent of global supply, to get rid of a glut that had built up since 2014 and that led to a price collapse.
OPEC wants to reduce oil inventories held by industrialized nations to their five-year average and is getting closer to that goal, although officials are starting to talk about looking at different metrics.
(Additional reporting by Henning Gloystein; Editing by Edmund Blair)