New York's main contract, WTI light sweet crude for June delivery, added 69 cents from Friday's close to USD 96.71 a barrel.
Brent North Sea crude for delivery in July gained 16 cents to USD 104.80 a barrel in London.
"It is a very quiet day in the markets due to holidays across several European countries while economic data is non-existent, meaning crude oil is driven more by technical buying and selling rather than the fundamentals today," said analyst Fawad Razaqzada at trading group GFT Markets.
Crude futures surged late last week after a better-than-expected reading on US consumer confidence boosted hopes for stronger energy demand in the world's biggest economy and sent Wall Street to new record highs on Friday.