According to David Pimental of Cornell University, the production of ethanol requires almost 30% more energy to produce than it provides as a fuel. Another study from UC Berkeley concluded that ethanol is less fossil fuel intensive that gasoling production, but has greenhouse emisisions similar to gasoline. Finally a researcher at MIT reports a slight advantage for gasoline, but one that can easily be overcome via technological breakthroughs in the near future. According to research from a Proceedings of the National Academy of Sciences study ethanol yields 25% more energy than the energy invested in its production, whereas biodiesel yields 93% more.
So it seems the jury is still out on the energy balance of ethanol, with a slight advantage on the positive side.
Natural Resources Research, vol 14 p65
Science, vol 311 p 506
Tiffany Goode, MIT (Graduate Student)
PNAS July 25, 2006 vol. 103 no. 30