Iraq has some of the world's largest oil reserves
The oil-for-food programme (OFF) was set up to allow Iraq to sell its oil in return for humanitarian relief, so it would not breach sanctions imposed after the first Iraq war.
The programme was administered by the United Nations and is now embroiled in a corruption scandal.
BBC News looks at the key events:
August 1990: The UN imposes sanctions on Iraq following the country's invasion of Kuwait.
March 1991: A UN mission to Iraq reports: "The Iraqi people may soon face a further imminent catastrophe, which could include epidemic and famine, if massive life-supporting needs are not rapidly met."
The UN proposes to allow Iraq to sell its oil in exchange for humanitarian goods without breaking the sanctions. The Iraqi government refuses.
April 1995: The UN Security Council adopts a resolution to establish an "oil-for-food" programme. Iraq refuses its terms.
December 1996: The programme is implemented and the first oil is exported. The first shipments of food arrive in Iraq in March 1997.
17 March 2003: All UN humanitarian staff are withdrawn from Iraq, two days before the start of the second war in Iraq.
November 2003: The oil-for-food programme is wound down and handed over to the Coalition Provisional Authority.
January 2004: An Iraqi newspaper publishes a list of 270 people from some 40 countries - including UN officials, politicians and companies - it alleges may have profited from the illicit sale of Iraqi oil during the OFF programme.
March 2004: The US General Accounting Office says it believes Saddam Hussein made $10bn of illicit gains from the programme between 1997 and 2002.
April 2004: The UN sets up a high-level inquiry into the allegations. Former US Federal Reserve chairman Paul Volcker is appointed to head the panel.
The US Congress and the Iraqi government set up their own inquiries.
October 2004: The UN inquiry gets $30m in funding from the programme itself. Mr Volcker says the allegations are serious and the investigation could take more than a year.
A report by the Iraq Survey Group, published on the CIA website, says Saddam Hussein's government netted $11bn from the deals.
It also accuses the former head of the oil-for-food programme, Benon Sevan, of benefiting from the corruption. Mr Sevan denies any wrongdoing.
November 2004: US Senate investigators say they believe Saddam Hussein made more than $21bn from illicit oil sales and kickbacks.
They believe $13.6bn came from selling oil to neighbour states keen to breach the sanctions, while $4.4bn was earned through kickbacks on humanitarian goods supplied through the programme.
Kofi Annan expresses disappointment that his son Kojo worked for Swiss-based Cotecna for four years longer than previously believed. Cotecna had a contract with the oil-for-food programme. Kojo Annan is said to have worked only for its West African operations.
January 2005: Iraqi-American businessman Samir Vincent appears in a US federal court as part of a criminal investigation into the scandal by the US Justice Department. Mr Vincent pleads guilty to being an illegal agent of Saddam Hussein's government and skimming money from the programme.
February 2005: Benon Sevan is accused of having repeatedly asked Iraqis to allocate oil to a particular company in an interim report by the UN inquiry.
Mr Sevan and another official, Joseph Stephanides, are suspended from the UN. Both deny any wrongdoing.
March 2005: Another interim report finds "significant" questions over the integrity of Kojo Annan's dealings. Kofi Annan is cleared of any wrongdoing, but is faulted over an "inadequate" inquiry into the affair.
April 2005: A Texas businessman, a Bulgarian and a Briton are indicted in the US for taking part in an alleged scheme to pay bribes to Saddam Hussein's regime in Iraq.
May 2005: US Senate investigations committee says British MP George Galloway and former French Interior Minister Charles Pasqua were rewarded with oil allocations by Saddam Hussein's regime. Both deny the accusation.
A few days later, the committee accuses Russian politician Vladimir Zhirinovsky, and former presidential aides Alexander Voloshin and Sergei Issakov, of receiving oil allocations in return for Russian lobbying on Iraq's behalf. Russia says it would be "unethical" to comment before the Volcker report is released.
June 2005: The UN inquiry says it is "urgently reviewing" new material on contacts between Kofi Annan and Cotecna. Two newly uncovered memos from the company say an executive met the head of the UN "and his entourage" and was told the firm "could count on their support" ahead of the award of an oil-for-food contract to the company. Mr Annan denies prior knowledge of Cotecna's bid for the contract.
August 2005: Benon Sevan resigns on the eve of the publication of the third report into the scandal. In a bitter letter to Kofi Annan, he denies any wrongdoing and says he has been sacrificed for political expediency. In the report, Mr Sevan is accused of receiving about $150,000 in cash bribes.
September 2005: The Volcker panel releases its final report, in which it condemns "illicit, unethical and corrupt" behaviour during the scheme, and blames the secretary general for mismanagement.
There is no evidence of wrongdoing by Kofi Annan, but he admits the affair is "deeply embarrassing" for the UN.