Brent North Sea crude for delivery in October fell 42 cents to $115.38 a barrel approaching midday trade in London.
New York's main contract, light sweet crude for October, dropped 21 cents to $89.13 a barrel.
Prices had risen sharply on Wednesday, closing up more than three dollars in New York, as stock markets rebounded and in the aftermath of a tropical storm which was still disrupting oil production in the Gulf of Mexico.
About 37 per cent of crude production in the Gulf of Mexico -- a key oil-producing region for the United States -- was closed on Wednesday because of Tropical Storm Lee, the US Department of the Interior said.
US inventory data published later on Thursday was expected to reveal a drop in crude stockpiles owing to the shutdown, analysts said.
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