Crude prices retreated Friday following a sharp rebound the day before.
Traders speculated that Saudi Arabian supplied less crude to the market was not a signal for production cuts.
Crude prices advanced Thursday as Saudi Arabia was said to reduce its crude oil supplies to the market in September.
Saudi Arabia, the world's biggest crude exporter, supplied 9.36 million barrels a day in September, down 328,000 from the previous month, Bloomberg reported Thursday.
The ample supplies in U.S. continued to weigh on crude prices. Crude stockpiles added 7.1 million barrels to 377.7 million barrels last week, beating market's expectation of an increase of 3 million barrels, said the Energy Information Administration Wednesday.
Markets are also closely following the impact of the Ebola virus risk on global economies.
A New York doctor who returned recently from West Africa was tested positive for Ebola late Thursday, becoming the city's first diagnosed case, sparking panic among New Yorkers.
Light, sweet crude for December delivery moved down 1.08 dollars to settle at 81.01 U.S. dollars a barrel on the New York Mercantile Exchange, while Brent crude for December delivery dropped 70 cents to close at 86.83 dollars a barrel.