Brent crude futures were down 89 cents, or about 1.1%, at $81.30 a barrel, while U.S. West Texas Intermediate crude futures slipped 83 cents, also about 1.1%, to $76.01 a barrel at 1239 GMT.

Last week, the major forces underlying the rally were the persistent threats to shipping in the Red Sea, Ukrainian strikes on Russian refineries and U.S. refinery maintenance, Tamas Varga of oil broker PVM told Reuters.

This has led to scarce availability of products, particularly in the middle of the barrel, he said.

"These factors have not subsided yet – and for this reason, I believe that what we see at the moment is only a retracement."

Logistics disruptions in the Red Sea continued on Monday, with Yemen-based Houthis saying they had targeted a cargo ship in the Red Sea, which they said was American.