What are the advantages of ethanol over petroleum-based fuels?

RK is correct. The process is maybe as much as 10-20% efficient. Under the best of conditions and a good design, it can produce 110 to 120 kcals of energy from 100 kcals input. The best way to think of it is that it converts a less than ideal transportation fuel into a transportation fuel. The energy input can be wood chips, coal, natural gas, or corn (or other things), none of which are great as a portable fuel, and produce a liquid fuel. It requires an enormous amount of water to produce ethanol. In areas where there is a lot of production, it drops the groundwater level dramatically. These are, by the way, reasons it will never be competitive as a fuel source, using corn. Sugar as a raw material, is much better. Bio-diesel also has a decent chance. Brazil uses sugar for ethanol and cheap soybeans for diesel. The US restricts acreage of sugar to prop up prices for beet farmers. The government always robs from one to pay the other, doesn't it?