As oil becomes scarce, the world needs new transportation fuels. As new fuel options develop we need means of assessing which are most effective at replacing petroleum. So far many scientists have used a measure called ‘net energy’.

The hydrogen economy is not a futuristic concept. The U.S. Department of Energy's 2006 Advance Energy Initiative calls for competitive ethanol from plant sources by 2012 and a good selection of hydrogen-powered fuel cell vehicles by 2020.