As Saddam Hussein pressed the United Nations oil-for-food relief program for more money that he used to buy banned weapons, an unwitting ally may have been the American driver. Almost until the eve of the invasion of Iraq in March 2003, American oil companies were among the largest purchasers of Iraqi crude oil. The role that the companies, including ExxonMobil and ChevronTexaco, played in the oil-for-food program is now coming under greater scrutiny in the wake of a report by the chief arms inspector for the Central Intelligence Agency that disclosed how extensively Mr. Hussein was abusing profits from the...