Some analysts have also anxious that steady USA supply could limit future gains after oil rose to a multiyear high in late May, and prices fell Wednesday on the back of rising US inventories.
Brent crude futures settled up $1.96 a barrel, or 2.6 percent at $77.32.
Crude prices came under pressure after data suggested Chinese demand was waning and concerns lingered about growing US output. West Texas Intermediate (WTI) crude futures were down 38 cents, or 0.6 percent, at $65.57 a barrel.
One of the key features of oil markets recently has been the widening discount of US WTI crude versus Brent CL-LCO1=R , which has nearly quadrupled since February to $11.40 per barrel, its steepest discount since 2015.
The group and Russian Federation are due to meet at its headquarters in Vienna on June 22 to discuss production policy."The June 22 OPEC meeting will now likely become the most important factor influencing (the) crude price", Jefferies said.
Balancing those expectations has been falling production in Venezuela, which has the world's biggest oil reserves and is a key supplier to American fuel markets.
China's May crude oil imports eased away from a record high hit the previous month, customs data showed, with state-run refineries entering planned maintenance.
The group and Russian Federation are due to meet at its headquarters in Vienna on June 22 to discuss production policy.
Three sources have told Reuters Venezuelan state firm PDVSA is considering declaring force majeure on some exports, after plummeting output and tanker bottlenecks at ports. A host of European oil firms have announced their intention to cease doing business with Iran as result of impending USA sanctions.
"This is occurring because of the rapid increase in production from USA shale coupled with the tightening of supplies elsewhere through the actions of OPEC and Russian Federation", said William O'Loughlin, investment analyst at Australia's Rivkin Securities. "$80 is a temporary ceiling for oil until we hear from OPEC".
The United States government has unofficially asked Saudi Arabia and some other OPEC producers to increase output, sources said on Tuesday.
"The oil price is being driven by OPEC and views on how much and how quickly "OPEC plus" will raise output", Energy Aspects analyst Virendra Chauhan said.
Further weighing on prices has been surging USA output, which hit another record last week at 10.8 million bpd.
Venezuela wrote to fellow OPEC members urging them to unite against US sanctions, echoing a similar letter from Iran, according to people with knowledge of the matter.