The West Texas Intermediate for October delivery dropped 14 cents to settle at 41.37 dollars a barrel on the New York Mercantile Exchange.
Brent crude for November delivery slid 36 cents to close at 44.07 dollars a barrel on the London ICE Futures Exchange, marking the lowest front-month contract settlement since July 31.
A slew of data from the world's largest economy provided a mixed picture, failing to boost market confidence.
U.S. services Purchasing Managers' Index dropped to 56.9 percent in August from the July reading of 58.1 percent, the Institute for Supply Management reported on Thursday, indicating a slower pace of growth.
U.S. initial jobless claims, a rough way to measure layoffs, fell to 881,000 in the week ending Aug. 29, following an upwardly revised 1.01 million in the prior week, said the Department of Labor.
Traders continued to pore through the U.S. crude supplies numbers.
U.S. crude oil inventories decreased by 9.4 million barrels during the week ending Aug. 28, the U.S. Energy Information Administration (EIA) reported on Wednesday. Analysts polled by S&P Global Platts had forecast a fall of 1.2 million barrels.
The EIA also said that U.S. crude oil production averaged 9.7 million barrels per day last week, 1.1 million barrels less than the previous week.
The data reflected a period during which Hurricane Laura shut output and refining facilities in the Gulf of Mexico.