Oil prices rose on Monday with traders shifting money into crude futures as the dollar weakened and on concerns that new U.S. sanctions against Iran could be extended to affect crude supplies.
But markets were held back by more signs of growing U.S. production and by worries that import demand in China could slow.
International Brent crude futures were trading at 57.01 dollars per barrel at 0620 GMT, up 20 cents from their last close.
U.S West Texas Intermediate (WTI) futures were up 19 cents at 54.02 dollars a barrel.