US benchmark West Texas Intermediate (WTI) for July fell 52 cents USD 59.78 a barrel, while Brent shed 51 cents to USD 65.05.
Prices jumped on Friday following a mixed US stockpiles report. The US government's Department of Energy revealed Thursday a healthy decline in crude oil and gasoline reserves - but also a rise in output that could aggravate the global oversupply.
However, dealers remain worried about demand as the global economy struggles to pick up the pace.
The cartel's decision in November to keep output at 30 million barrels a day helped fuel a massive sell-off in the black gold that saw prices plunge more than 60 per cent between June and January.
"Production is going to have to come down to prevent oil prices falling away," Ric Spooner, a chief analyst at CMC Markets in Sydney, told Bloomberg News. "Not only is Saudi Arabian output steady but we also saw US production flicking up again. That's why we're constrained on the upside.