Oil prices surged nearly $2 a barrel on Monday to their highest settlement levels in over a month, adding to last week's gains as investors grew more optimistic on the demand outlook.

U.S. West Texas Intermediate crude futures gained by $1.88, or 2.4%, to settle at $80.33 a barrel, the highest since the end of April. Global benchmark Brent crude gained $1.63, or 2%, to $84.25 a barrel, also the highest since April.

Last week, both benchmarks posted their first weekly gain in four weeks after reports from the OPEC+ producer group, the International Energy Agency and U.S. Energy Information Administration raised confidence that oil demand will improve in the second half of the year and help inventories draw down.

Reassurances from OPEC+ that a plan to raise supplies from the fourth quarter of this year could be paused or reversed based on market conditions also helped prices firm. That plan, unveiled after the group's meeting on June 2, had led to a sharp selloff in prices.

"The outlook for strong fuel demand into the coming quarter and Saudi reassurance about the October hike being subject to prevailing conditions and added focus on quota breakers to bring production down and into line all seems to be supporting," said Ole Hansen of Saxo Bank.

Investors last week repurchased some of the petroleum they had sold the week before, data from the Commodity Futures Trading Commission showed on Friday.

"Those funds who thought we were heading into a production battle, had their concerns quickly assuaged when OPEC+ members went on a PR campaign to assure the world their changes to production would be market dependent," said Alex Hodes, oil analyst at brokerage firm StoneX.