New York's main contract, light sweet crude for delivery in July, eased 15 cents to $83.17 a barrel.
Brent North Sea crude for July rose 38 cents to $97.52 a barrel in London midday deals.
OPEC member nations were at odds on Wednesday over whether to cut the cartel's oil output to help firm crude prices that have tumbled this year on weak demand, over-supplies and the eurozone debt crisis.
The Organization of Petroleum Exporting Countries, which supplies about one third of global oil, was to hold a regular ministerial meeting in Vienna on Thursday following a 25-percent slump in crude prices since March.
The International Energy Agency, which represents oil consuming countries, said on Wednesday that the eurozone sovereign debt crisis, China's economic slowdown and high energy supplies combined to depress crude prices in May.
But it warned that energy costs remained historically high, crimping growth.
The IEA also cut its 2012 global demand forecast to 89.9 million barrels per day from the 90 mbpd given in its previous monthly report.
Meanwhile Iran said its looming oil embargo, related to the country's controversial nuclear programme, would destabilise the global oil market.
"Unfortunately the issue of imposing sanctions ... is being considered by Europe," Iranian Oil Minister Rostam Qasemi said on Wednesday in Vienna.
"This politically-motivated approach will damage the stability of both the oil market and the world economy," said Qasemi, who represents OPEC's second biggest crude producer after Saudi Arabia.
"Unilaterally imposing sanctions as a means to attain a political objective are imposing constraints on the oil industry. This will result in an unstable oil market and ultimately lead to a sharp swing (higher) in the price of oil," he added.
The European Union was preparing to impose an oil embargo on Iran on July 1, unless diplomatic talks over its disputed nuclear programme saw progress.
Western countries and Israel believe Iran is trying to develop a nuclear bomb under cover of its civilian programme but Tehran insists its purpose is merely peaceful.
