Net Energy Balance (NEB).Despite our use of expansive systemboundaries for energy inputs, our analyses show that both corngrain ethanol and soybean biodiesel production result in positiveNEBs (i.e., biofuel energy content exceeds fossil fuel energyinputs) (Fig. 1; see also Tables 7 and 8, which are published assupporting information on the PNAS web site), which reinforcerecent findings (1–5). Although these earlier reports did notaccount for all of the energy inputs included in our analyses,recent advances in crop yields and biofuel production efficien-cies, which are reflected in our analyses, have essentially offsetthe effects of the broad boundaries for energy accounting that wehave used. Our results counter the assertion that expandingsystem boundaries to include energetic costs of producing farmmachinery and processing facilities causes negative NEB valuesfor both biofuels (6–8). In short, we find no support for theassertion that either biofuel requires more energy to make thanit yields. However, the NEB for corn grain ethanol is small,providing25% more energy than required for its production.Almost all of this NEB is attributable to the energy credit for itsDDGS coproduct, which is animal feed, rather than to theethanol itself containing more energy than used in its produc-tion. Corn grain ethanol has a low NEB because of the highenergy input required to produce corn and to convert it intoethanol. In contrast, soybean biodiesel provides93% moreenergy than is required in its production. The NEB advantage of soybean biodiesel is robust, occurring for five different methodsof accounting for the energy credits of coproducts (see Table 9,which is published as supporting information on the PNAS website).