New York's main contract, light sweet crude for January delivery, gained 14 cents to $89.33 a barrel after closing at $89.19 on Friday, its highest point since October 9, 2008.
Brent North Sea crude for delivery in January advanced 17 cents to $91.59 a barrel, after it also hit two-year highs on Friday.
"It's really momentum from last Friday carrying forward to trading this morning," said Victor Shum, senior principal of Purvin and Gertz energy consultants in Singapore.
Oil prices had surged last Friday as traders largely ignored deeply disappointing US employment numbers in favour of a slumping US dollar.
A weak greenback makes dollar-traded commodities more attractive for investors.
Shum added that oil markets were also cheered by strong energy demand fuelled by a cold snap in Europe that was only just beginning to ease.
"It's really the optimism in the market about the fuel demand," he told AFP.
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