At popular mechanics. It's pretty good, offering a good amount of data on each alternative. Ethanol is #1 as most likely to suceed gas. The PM people point out its emission neutral, due to the very simple formula CO2+H2O = glucose+O2. The glucose is then converted to ethanol by yeast fermentation, and burning releases the CO2 into the atmosphere. They ignore the ineffiency of these processes, but the point is that it will release far less CO2 than gas.