The use of energy accounts for a major fraction of all anthropogenic emissions of greenhouse gases (GHGs), and in most industrialized countries transportation fuel use produces a major fraction of all energy-related emis sions. In the U.S., for example, emissions of GHGs from transportation accounts for over 27 percent of anthropo genic GHG emissions, while globally, transportation contributes approximately 14 percent of GHG emissions1.Figure 1 shows the various sources of global GHG emissions from human activity and which specific GHGs are ultimately emitted.