Paul Volcker said after six months of work, documents found at the Iraqi oil ministry include the names of several prominent politicians in France, Russia and elsewhere who allegedly received illegal Iraqi oil from Saddam Hussein.
He said so far investigators have had "good cooperation," but as the web of corruption peels away, "a certain amount of friction" was being encountered.
"When you begin to appraise and find out about a particular company that was really corrupt, and the people who may have been behind that, then you will get some resistance, whether by government or otherwise," he said.
The U.S. Congress has four congressional committees also investigating, as well as two New York law enforcement agencies, which Volcker said was not working out well.
"We'd like to think that they are complementary (to the investigation). But they are not. They are competing," he said.