This document discusses biofuels as a potential solution for reducing carbon emissions from transportation. It outlines three generations of biofuel technologies: 1) First generation biofuels like biodiesel and bioethanol require significant land use but have relatively low energy outputs. 2) Second generation biofuels could use non-food crop biomass as feedstock in more efficient processes. 3) Third generation microalgal biofuels have the highest potential energy outputs and land use efficiencies of all options discussed.