"One fear I would have is that the U.S. has a hidden thought to remain in Iraq," Blix, the former chief of the U.N. inspection team looking for weapons of mass destruction in Iraq, told Australia's ABC radio.
Blix was in Australia accepting the Sydney Peace Prize.
"One reason why they wanted in was that they felt they must leave Saudi Arabia. After the Gulf War in 1991, they left their troops in Saudi Arabia to protect pipelines," he said. "And when they felt they could no longer stay in Saudi Arabia, Iraq was the next best place because it was more secularized than Saudi Arabia and had the second biggest oil reserves in the region."
In September former U.S. Federal Reserve Chairman Alan Greenspan caused a stir when he wrote in his new book about the Iraq oil-war connection.
"I am saddened that it is politically inconvenient to acknowledge what everyone knows: The Iraq war is largely about oil," Greenspan wrote toward the end of "The Age of Turbulence: Adventures in a New World."
Iraq has the world's third-largest proven oil reserves and is believed to have twice as much of yet undiscovered oil.
But with the main rationale for the war -- Saddam Hussein's weapons of mass destruction and links to al-Qaida -- now debunked, the anti-war community is looking at motives.
U.S. officials deny such allegations.