A life-cycle analysis is often used to demonstrate that one product is environmentally superior to another and to identify stages where a reduction in use of resources and emissions can be achieved. This type of analysis is ideal to determine the impact of biofuels on global warming using a WTW analysis. A WTW analysis combines the fuel production system, well-to-tank (WTT), the energy and GHGs associated with delivering the fuel to the vehicle’s tank. The second part is tank-to-wheel (TTW), the energy expended and GHGs produced by the vehicle power train. These are com­bined to produce the WTW values.

In a recent study, the Joint Research Centre has given the energy use and GHG emissions in a WTW for a number of fuels including ethanol and biodiesel. The study was not a complete life-cycle analysis as it does not include the energy used and GHG emissions produced in building the production facilities and vehicles. Nevertheless the data illustrate the problems with some biofuel sources.