New York's main contract, light sweet crude for March delivery, dropped 10 cents to $77.64 a barrel.
London's Brent North Sea crude for delivery in March fell 20 cents to $76.12 a barrel.
Analysts polled by Dow Jones Newswires said they expect US crude reserves to show a rise of 1.9 million barrels last week when the Department of Energy (DoE) releases its report later Thursday. A rise in stocks is seen as an indication of weak demand.
Gasoline stocks are seen increasing by 1.3 million barrels, the poll said. The DoE is releasing its report one day later than normal owing to a US bank holiday on Monday.
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"If the report is showing a build (in stockpiles) like everybody else expected, prices could keep going down," said Clarence Chu, an oil trader with Hudson Capital Energy in Singapore.
Crude prices have been under pressure after comments yesterday by top Beijing regulator Lim Mingkang that China would rein in credit after explosive growth last year as the world's most populous nation moves to cool its red-hot economy.