West Texas Intermediate futures for November delivery fell to $46.23 (-0.28%), while Brent crude declined to $48.90 (-0.37%) as weak data on China's manufacturing intensified concerns over demand from the second-biggest oil consumer. A preliminary report from Markit Economics and Caixin Media showed on Wednesday that China's manufacturing sector had fallen to a six-and-a-half-year low of 47.0 in September. Economists had expected a 47.5 reading after 47.3 reported previously. A reading below 50 suggests contraction.

Late Tuesday, the American Petroleum Institute reported that U.S. crude-oil inventories fell 3.7 million barrels for the week ended September 18. This report temporarily boosted prices. The Energy Information Administration data will be released later today.

Thirteen analysts surveyed by the Wall Street Journal expect U.S. oil stocks to have fallen by 100,000 barrels, on average, in the same week.