Oil prices fell on Monday, giving up earlier gains, squeezed by plentiful supply and U.S. firms in particular increasing exports in competition with traditional producers from the Middle East in key markets like Asia.
International Brent crude oil futures were at $66.88 a barrel at 0449 GMT, down 24 cents, or 0.4 percent, from their last close, Reuters said.
They ended Friday little changed after touching their highest since Nov. 16 at $67.73 a barrel.
U.S. West Texas Intermediate (WTI) crude futures were at $57.11 per barrel, down 15 cents, or 0.3 percent, from their last settlement. WTI futures climbed 0.5 percent on Friday, having marked their highest since Nov. 16 at $57.81 a barrel.
Traders said the dips were a result of ample oil supply amid surging exports from the United States, forcing other producers especially in the Middle East to start offering their crude at discounts.
Under pressure from a surge in U.S. supply, Abu Dhabi's flagship Murban crude has sold at a discount in Asia to its official selling price (OSP) for four straight months - the longest stretch in nearly two years.
Cargoes bought for loading in the first four months of 2019 were sold at discounts ranging from 5 cents to 40 cents a barrel, even as producer Abu Dhabi National Oil Company (ADNOC) cut the grade's benchmark price for four consecutive months.
U.S. crude oil production has hit a record 12 million barrels per day (bpd), an increase of more than 2 million bpd since early 2018. Exports hit a record 3.6 million bpd this month.
The surge in U.S. oil output counters efforts led by the Middle East-dominated Organization of the Petroleum Exporting Countries (OPEC) to cut output in order to tighten the market and prop up prices.
The OPEC-led cuts as well as U.S. sanctions against Iran's and Venezuela's oil exports pushed oil prices to 2019 highs last week.