Benchmark West Texas Intermediate crude for May delivery slid 30 cents to close at US$103.75 on the New York Mercantile Exchange. On Monday, the Nymex contract rose 31 cents.
Brent crude, a benchmark used for international varieties of oil, dropped 33 cents to US$108.74 on the ICE Futures exchange in London after hitting a six-week high.
Officials from the U.S., Russia, Ukraine and the European Union are set to meet in Geneva on Thursday for negotiations aimed at persuading Russia to back off in Ukraine following its annexation of Crimea.
Failing that, EU leaders could meet as early as next week to decide on tighter sanctions on Russia, a major producer of oil and gas that has been accused of fomenting unrest in eastern Ukraine.
Expectations of rising U.S. crude oil stockpiles also weighed on prices.
Data for the week ended April 11 is expected to show an increase of 2.4 million barrels in crude oil stocks, according to a survey of analysts by Platts, the energy information arm of McGraw-Hill Cos.
Meanwhile, continued uncertainty about the reopening of oil export terminals in Libya, a key supplier of high-quality crude to European refineries, kept a floor under prices.
In other energy futures trading on the Nymex, wholesale gasoline was flat at US$3.04 a U.S. gallon (3.79 litres, heating oil lost a penny to US $2.98 a gallon and natural gas rose one cent to US$4.57 per 1,000 cubic feet.
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