Investing.com - Oil edged lower Monday after earlier gains on ongoing tensions between the U.S. and Iran.
Investors were also weighing up the possible impact of a rise in the number of rigs operating in the U.S.
Brent crude was off 18 cents, or 0.32%, at $56.63 at 08:00 ET. U.S. crude shed 2 cents, or 0.04%, to $53.81.
The U.S. imposed fresh sanctions on Iranian companies in response to ballistic missile testing by Tehran.
Baker Hughes figures Friday showed an increase in the U.S. rig count of 17 to 583.
That was the highest level since October 2015.
Increased North American shale activity could offset the impact of agreed cuts by other major producers.
OPEC and non-OPEC producers have agreed to cut output by 1.8 million barrels a day in the first half of this year.