Benchmark West Texas Intermediate crude for April delivery dropped $1.09 to close at US$100.03 a barrel on the New York Mercantile Exchange, the lowest price in a month.
Brent crude, used to set prices for international varieties, rose 47 cents to US$108.55 on the ICE Futures exchange in London.
Investor expectations that the U.S. Energy Department will report an eighth straight weekly increase in oil supplies put pressure on prices.
Data for the week ended March 7 is expected to show an increase of 2.3 million barrels in crude oil stocks and a decline of 1.8 million barrels in gasoline stocks, according to a survey of analysts by Platts, the energy information arm of McGraw-Hill Cos.
In other energy futures trading on Nymex, wholesale gasoline gained two cents to US$2.97 a U.S. gallon (3.79 litres), heating oil was down one cent at US$2.96 a gallon and natural gas lost five cents to US$4.61 per 1,000 cubic feet.
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