Iraq made more than $21bn (£11.3bn) from illicit oil sales and kickbacks in breach of UN sanctions, the US Senate has heard.
Smuggling oil provided the main source of corrupt revenue
The figure is double the $10bn quoted in a CIA report on Iraqi weapons.
About $13.6bn came from selling oil to neighbour states keen to breach the sanctions, Senate investigators said.
But about $4.4bn was earned through kickbacks on humanitarian goods supplied through the UN's oil-for-food (OFF) programme, they said.
Previous reports such as the CIA's - produced by a 1,200-strong team led by Charles Duelfer, one of four witnesses testifying - have alleged that firms, government ministers and senior UN officials benefited from the corruption.
Among them are the former head of the oil-for-food programme, Benon Sevan, and a number of French politicians and companies. They have denied the allegations.
The investigators working for the Senate governmental affairs committee said they had reached the larger figure through access to newly available documentation, and by considering the whole period from 1991 to 2003.
US SENATE FINDINGS
Out of a total of $21.3bn, $17.3bn came from abuses during the oil-for-food programme. Within this:
$9.7bn from oil smuggling
$4.4bn in kickbacks from contracts for humanitarian goods
$2.1bn from substituting low-quality goods for high-quality ones
$403m from overseas investment of illicitly earned funds
$241m from surcharges on oil sales
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Their findings calculated that Iraq raised $3.9bn through oil smuggling between the end of the 1991 Gulf War and December 1996.
That was when the OFF programme began, allowing Iraq to sell oil and use the proceeds - deposited in a UN Security Council-controlled fund - to buy food, medicines and humanitarian supplies.
But Iraq was permitted to draw up its own contracts, the investigators said, enabling it to sidetrack $17.3bn out of the $64bn programme.
"The magnitude of fraud perpetrated by Saddam Hussein in contravention of UN sanctions and the OFF programme is staggering," said Senator Norm Coleman, chairman of the permanent subcommittee on investigations.
"This is like an onion - we just keep uncovering more and more layers."
The huge sums raised from smuggling saw neighbouring countries including Syria, Jordan and Turkey conclude secret deals - called protocols - to import large quantities of oil, the investigators said.
But other oil revenue came from selling certificates allowing the holder to sell on oil rights and charge a per-barrel commission on them.
Charles Duelfer's team published a 1,000-page report in October
Some of these certificates, the investigators said, went to groups such as the Mojahideen-e-Khalq, a group aiming to overthrow neighbouring Iran, and to the Popular Front for the Liberation of Palestine.
Others went to journalists or foreign officials, the investigators said.