West Texas Intermediate crude for May delivery rose seven cents to US$104.37 a barrel on the New York Mercantile Exchange after a three-day holiday weekend.
Markets were on edge at the possibility of European or U.S. sanctions that might disrupt Russian oil exports. Tensions got worse after an Easter morning shooting at a checkpoint manned by pro-Russian insurgents.
Upward pressure on oil prices was offset last week by a U.S. Energy Department report that showed an increase of 10 million barrels of crude oil supplies, the largest in 13 years.
Brent crude, an international benchmark, rose 42 cents to US$109.95 a barrel in London.
In other energy futures trading in Nymex, wholesale gasoline rose three cents to US$3.087 a U.S. gallon (3.79 litres), heating oil was flat at US$3.01 a gallon and natural gas fell four cents to US$4.697 per 1,000 cubic feet.
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