"Not included in this study, but something I've read from various other sources, is that at the moment it takes more energy from burning petroleum to produce ethanol than the energy the ethanol returns. I can believe that this can be overcome in the future, but there it is for today -- burning ethanol increases petroleum useage... and AFAIK, farm machinery isn't generally smog-controlled."


I'd be interested to read your sources on that. From what I've read, it is actually less expensive to produce, but one worry is how much land can you expect to take over for the production of it at present consumption rates. Here are two interesting articles:

http://www.usatoday.com/tech/news/2006-03-28-brazil-ethanol-cover_x.htm?POE=TECISVA

http://www.centredaily.com/mld/aberdeennews/news/14470921.htm?source=rss&channel=aberdeennews_news

One of the problems in the US is that corn is hugely subsidized, and not the most efficient producer of sugar-based engergy. Farming in the US is heavily dependant on huge machinery for the harvest also, whereas Brazil still uses a lot of cheap human labor. Ethanol is a bio-fermentation process also, so it doesn't take nearly the energy in purely processing it as petro-oil does in cracking it with intense heat in towers (fueled by petroleum). I'm not trying to argue with you -- just sort it out in my own head. It seems clear that ethanol could never completely replace gas, nor biodiesl, because of the ammount of land that would be required at present american consumption rates.

Gas is very energy dense and also doesn't required any arrable land. It's kind of the crack or heroine of the modern industrial age... very tough to ween off of.