THE US went to war in Iraq motivated largely by oil, former US Federal Reserve chairman Alan Greenspan says in a memoir to be released today.

"I am saddened that it is politically inconvenient to acknowledge what everyone knows: the Iraq war is largely about oil," he writes.

Mr Greenspan's book The Age of Turbulence: Adventures in a New World also criticises President George Bush for not responsibly handling the nation's spending and racking up big budget deficits.