Depending on the goal and scope of the LCA, choices regarding system definition and boundaries are more or less accurate. The goal may be process design-, operation-, or policy-oriented. While the definition of the system is more detailed in case of design or oper­ation improvement, the flowchart of biofuel pathways is simplified for policy-related LCA. In that latter case, the system boundaries are adapted to the purpose. For instance, if the intent is the comparison of various pathways of the same biofuel (e. g., bioethanol), a WtT LCA is appropriate because the pathways do not affect the performance of the fuel combustion in the vehicle’s engine. The situation changes dramatically if the LCA intends to compare selected biofuels with their fossil substitutes, for example, bioethanol blends versus gasoline or more generally when different kinds of fuels and blends are compared. In these cases, the utilization stage plays a crucial role as the energy need in the vehicle tank for a given ser­vice (e. g., 100 veh. km) depends on the combustion performances that in turn vary from one blend to the other. Ignoring this important factor even for simplicity will lead to implicit assumptions on the combustion performances and therefore may induce inconsistency.

However, several authors used WtT boundaries while comparing GHG emissions of biofuels and fossil fuels (e. g., ADEME-DIREM-PWC, 2002; Elsayed et al., 2003). In other stud­ies, the WtT was only a step for a complete WtWs assessment (e. g., Beer and Grant, 2007; CONCAWE-EUCAR-JRC, 2008; EMPA, 2007a; GM-LBST, 2002; Gnansounou and Dauriat, 2004; VIEWLS, 2005). Other aspects concerning the system definition and boundaries are the inclusion or not of land-use change and coproducts as part of the system. These two issues are addressed later on.