Former Federal Reserve chairman Alan Greenspan, for years an inscrutable seer on the economy, is causing a stir by alleging in his new memoir that "the Iraq war is largely about oil."

Greenspan, who as head of the US central bank was famous for his tight-lipped reserve, is uncharacteristically direct in "The Age of Turbulence: Adventures in a New World," also accusing President George W. Bush of abandoning Republican principles on the economy.

"I'm saddened that it is politically inconvenient to acknowledge what everyone knows -- the Iraq war is largely about oil," he wrote in reported excerpts of the book, which is set for release on Monday.