Oil resumed its slide on Monday as investors remained uncertain whether producing nations will extend an OPEC-led output cut beyond the end of June in an effort to reduce a global glut of crude.
On Sunday, a committee of ministers from OPEC and outside producers agreed to look at prolonging the deal, stopping short of an earlier draft statement that recommended keeping the measure in place.
Oil prices have been falling since the middle of the month, as a spate of reports showing stronger-than-expected growth in U.S. inventories sparked selling from speculators that had build record long positions in crude futures.
Last week's futures data showed speculators were still unwinding long positions, or bets that prices will rise, as high U.S. inventories offset cuts from other oil producers. Long positions as of last Tuesday were at their lowest since December.
A number of ministers from the Organization of the Petroleum Exporting Countries and other producers met in Kuwait to review progress of their supply cut.
In December, OPEC and 11 other producers including Russia agreed to reduce combined output by almost 1.8 million barrels per day in the first half of this year.
While many in OPEC have called for prolonging the curbs, Russia has been less definitive. Energy Minister Alexander Novak said on Sunday it was too early to make that call.
"We would see the relative lack of reaction in the price perhaps as a reflection of some disappointment that nothing more concrete was forthcoming," analysts at JBC Energy said in a report, referring to the conclusion of Sunday's talks.
There is "increasing skepticism" in the market as to whether a rollover of the cuts can be agreed, JBC added.
Oil also came under pressure from further evidence that the OPEC-led supply cut had lifted prices enough to help boost output in the United States.
U.S. drillers added oil rigs for a 10th week in a row, data from energy services firm Baker Hughes showed on Friday.
Still, Goldman Sachs said the market was rebalancing and it may not be necessary to keep output curbed.