Oil fell Monday as a jump in the U.S. rig count outweighed an upbeat output cut compliance meeting.
Brent crude shed 48 cents, or 0.87%, to $55.01 at 07:45 ET. U.S. crude lost 62 cents, or 1.16%, to $52.60.
Baker Hughes U.S. rig count data Friday showed a jump of 29 to 551, the highest level in 14 months.
That could point to higher U.S. shale output, which could offset the positive impact of the output cuts.
OPEC and non-OPEC producers held a meeting on the implementation of the cuts over the weekend.
The accord calls for a reduction of some 1.8 million barrels a day in the first half of this year.
Saudi Energy Minister Khalid al-Falih estimated the level of compliance at already 80%.