Brent crude was up by 7 cents to $79.38 a barrel by 0425 GMT, while U.S. West Texas Intermediate (WTI) crude rose 11 cents to $75.77 a barrel.
China's manufacturing activity unexpectedly fell in April, official data showed on Sunday, the first contraction since December in the manufacturing purchasing managers' index.
China's industrial and economic recovery from the coronavirus pandemic was expected to boost demand this year.
"Crude oil fell after weak economic data from China raised concerns about a patchy recovery," said analysts in an ANZ Research note, referring to China's manufacturing activity data.
Meanwhile, a Monday poll showed that U.S. crude oil stockpiles are expected to have fallen for a third consecutive week, providing some support to the market.