After the invasion, Iraqi production had slumped to between 1.7 million and two million barrels a day, the IEA said.
"While few would have predicted such an improvement in Iraqi security and output since September, the additional oil has been as welcome for the international market as it has been for Iraqi finances," the report said.
The report also said that production levels could be sustained or may even rise in the next few months, howver it said attacks on oil facilities could still pose a threat to oil output.
"Though the increase has been dramatic, the market continues to recognise the propensity for ongoing security issues and output volatility," it said.
Al Jazeera's John Cookson in the Iraqi capital, Baghdad, also said that the figure had to be put in perspective, as Iraq has larger oil reserves than Saudi Arabia, which nonetheless manages to pump more than nine million barrels a day.
However, he said the effect of this increased production was being felt economically on the streets of Baghdad, where Iraqis are increasingly exchanging the US dollar for Iraqi dinars.
Meanwhile, the IMF said on Saturday that Iraq had cleared ahead of schedule a $471m loan granted to the nation after the US-led invasion.
The Iraqi government repaid the loan ahead of an IMF meeting on Wednesday to discuss the country's new loan requests.
"Iraq's ability to repay the IMF ahead of schedule reflects its strong international reserve position against a background of high oil prices," Dominique Strauss-Kahn, the IMF managing director, was quoted by AFP as saying.