New estimates at the giant West Qurna and Zubair fields helped push the total figure to 143 billion barrels, but some analysts said they were skeptical about the massive revision and were not expecting OPEC to deal with the Iraqi quota until Baghdad manages to raise production and exports.

"The oil reserve is for 66 discovered oilfields in Iraq, and there are many others that have not been discovered yet," Oil Minister Hussain Al-Shahristani. "It is expected this figure will be increased when these oilfields are discovered.

He said West Qurna was now the world's second-largest field and added that the return of global oil firms to Iraq has help boost oil reserves. The Oil Ministry put Iraq's unrecoverable reserves at 505.4 billion barrels.

"The new proved reserves figure will entrench Iraq's position at OPEC and in the future help Iraq to get a higher export quota in OPEC," Falah Al-Amri, Iraq's OPEC delegate, told Reuters.

Al-Shahristani said Iraq's partners in the Organization of the Petroleum Exporting Countries would need to come up with a new mechanism to determine production quotas for OPEC members but the issue was not being discussed.

"We will not discuss the Iraqi quotas issue with OPEC now. This case has been delayed," Al-Shahristani said.

Iraq's reserves revision is likely to revive debate about how much oil the world has left. Companies have made numerous attempts to misreport reserves in the past, and analysts are skeptical about the reliability of Middle East reserves data in general.

"I don't think it's possible accurately and confidently to look at the reserves for many Middle Eastern countries with a great deal of confidence," said Paul Harris, a natural resource analyst at Bank of Ireland, referring to numerous previous substantial revisions to reserves by OPEC members.

Some countries, including some OPEC members, are in fact reporting total oil reserves discovered instead of oil still to be extracted, several analysts have said.

But Al-Shahristani said the old figure of 115 billion barrels was actually 110 billion because 5 billion had been consumed.