A new study co-authored by Cornell ecologist David Pimentel concludes that turning biomass into liquid fuel consumes substantially more energy than the fuel generates. Producing ethanol from corn, for example, takes 29 percent more energy than you get by burning the ethanol. The study found that soybean-based biodiesel is similarly wasteful, while liquid fuels made from wood, switch grass, and sunflower plants are even worse.
Ron Bailey cited Pimentel's work in a 2003 Reason Online critique of ethanol subsidies.
[Thanks to Nicolas Martin for the link.]