Gas

Biofuel is cool. Britain is planning on blending 5% biodiesel with their gasoline and diesel fuel (which is a small enough amount that ordinary engines won't require modification) by 2010, a strategy also endorsed by the American truckers, and various Midwest governors are touting their alternative-fuel vehicles.

Unhappily, conventional agriculture uses lots of petroleum in its own right, so it's not clear how much less fossil fuel we're actually burning; earlier this year, a study by David Pimentel and colleagues, focusing on corn alcohol, was the latest to find no savings at all for the cases they examined.