Brent crude was down 17 cents at $52.04 a barrel by 0837 GMT.
Both benchmark prices started the day in negative territory after industry data from the American Petroleum Institute (API) estimated that U.S. crude stocks had risen by 882,000 barrels in the week ending May 12 to 523 million barrels.
Overnight, crude futures settled higher on Wednesday, as investors cheered the release of a bullish report from the Energy Information Administration (EIA), showing USA crude inventories fell for a sixth-straight week.
Meanwhile, gasoline inventories dropped by only 0.413 million against expectations for a draw of 0.731 million barrels while distillate stockpiles fell by 1.94 million barrels, compared to expectations of a 1 million decline.
OPEC and its oil-producing partners may have to do more than merely extend their petroleum-output cuts to achieve their goal of rebalancing global supply and demand, the International Energy Agency said.
Brent reached US$52.63 a barrel and WTI rose as high as US$49.66 on Monday after Saudi Arabia and Russian Federation agreed on the need to extend output curbs by members of the Organization of the Petroleum Exporting Countries and other producers.
"The agreement by OPEC to extend cuts into 2018 is critical", said AB Bernstein in a note.
OPEC agreed to slash the output by 1.2 million barrels per day from January 1, with top exporter Saudi Arabia cutting as much as 486,000 barrels per day.
He cautioned, however, that the market may expect deeper cuts to keep prices elevated, particularly with USA production still rising.
Goldman said that beyond the ongoing rise in United States oil production, which is up over 10 per cent since mid-2016 to 9.3 million bpd, output will increase by Opec members who were exempt from the cuts, or where supply disruptions had ended, including Libya and Nigeria.
The current oil minister, Bijan Zanganeh, speaking on May 6, said he believed producers were likely to extend the OPEC-led deal although he did not give a timeframe, and added $55 was a suitable price for oil.
Adding to concerns of ongoing supply increases, a report said North Sea oil production, which has always been seen as in terminal decline, is expected to jump by a net 400,000 bpd, or about a fifth of total output, in the next two years as producers improve operational efficiency.
Shipping data in Thomson Reuters Eikon shows that US crude exports to Asia have soared from a handful of tankers a quarter throughout 2015 and 2016 to 10 tankers in the first quarter of 2017 and that figure is expected to rise.