Bingo. There have been studies on the EROEI (Energy Return on Energy Invested) on corn ethanol, and while results vary somewhat, the consensus seems to be that while the EROEI is positive, it's barely so. Maybe around 1.2-1.5, I don't recall, been a while since I looked into it. That is, to get around 1.5 units of energy in the form of corn ethanol, you'll need 1 unit of energy embodied in fertilizer, diesel fuel for agricultural machinery, natural gas for the distillation etc.