Oil prices fell Monday as Iran and major western powers said they were closer than ever to a landmark nuclear deal that would lift sanctions and hike Tehran's crude exports.
A forecast by the International Energy Agency (IEA) for slower world oil demand growth next year and slumping Chinese trade data were also weighing on the market, analysts said.
US benchmark West Texas Intermediate for August delivery was down 23 cents at $52.51 barrel.
Brent North Sea crude for August slid 70 cents to stand at $58.03 a barrel in London afternoon deals.
Iran's President Hassan Rouhani will address the nation on state television on Monday night, a media official told AFP, amid reports a nuclear deal with world powers could be imminent.
Rouhani's appearance is scheduled for around 10:00 pm (1730 GMT) the official said, noting that the president would talk about the negotiations taking place in Vienna.
Any deal to curb what the West suspects as Iranian efforts to build an atomic bomb will result in the lifting of punishing economic sanctions, allowing the country to resume oil exports.
More Iranian oil however will add to a supply glut, which has depressed prices.
"Reports... have suggested that a comprehensive 'in-principle' agreement has been reached over the main issues, with only technical considerations remaining unresolved," said Nicholas Teo, market analyst at CMC Markets.
"This may once again move the needle for crude," he added in a market commentary.