Investors, such as Microsoft's Bill Gates, are sitting on billions of dollars in losses after buying into the corn-based ethanol industry that George W. Bush embraced as the answer to US energy woes.

Six of the biggest publicly traded US ethanol producers have lost more than $8.7bn (£5bn) in market value since the peak of the boom in mid-2006 and the beginning of this month, according to an analysis by the Financial Times. The boom followed a 2005 law requiring refiners to mix billions of gallons of the biofuel with petrol.