Iraq has raised the level of the oil reserves it claims to own by 24% in its first revision since the change of regime in 2003.
The country has 143.1bn barrels of known and extractible oil, up from the 115bn barrels previously estimated.
If correct, the revision means that Iraq now has bigger oil reserves than neighbouring Iran.
Under Saddam Hussein, sanctions and political isolation meant little new exploratory work was undertaken, but Iraq has issued two rounds of international oil licences, and launched a big increase in exploration efforts in the last two years.
Announcing the new figures, the Iraqi oil minister, Hussein al-Shahristani, said he expected further increases as continuing exploration yields more results.
The minister also said that his country would now officially inform the Organisation of Petroleum Exporting Countries (Opec) of its findings, so that the new reserves figure can obtain international recognition; Iraq may be pushing for a bigger share of Opec's oil production.
Iraq aims to increase its oil exports to 10-12 million barrels per day in the next five to 10 years, but this will require sustained investment in infrastructure to extract and transport the crude.
The new proven reserves figure excludes oil located in the autonomous province of Kurdistan in the north of the country, according to the oil minister.
"The Kurdish regional government did not supply us with the latest developments of their activities," complained Mr al-Shahristani.
"We are surprised that they supply oil companies with this information, but do not inform the oil ministry or the federal government."
The reserves are mainly located in the Shia-dominated south of the country. Iraq's biggest oilfield - West Qurna - is the world's second largest, with 43bn barrels, according to the oil minister.
He said that a further 33.5bn barrels of oil are known to exist, but are [currently considered to be] unrecoverable.