Due to increasing oil prices and climate change concerns, biofuels have become more important as potential alternative energy sources. It is an open question as to which types of biofuels have the best yield potentials, characteristic properties and environmental consequences for providing the largest contribution to future energy requirements. Apart from the quality aspects, the question of quantity is very important, i.e., yields of biomass raw materials from agriculture and forestry as well as the conversion efficiencies/yields of the conversion process to automotive fuels. The most widely used biofuel forms today are fatty acid methyl esters and ethanol. However, in the future it is possible that synthetic hydrocarbons and hydrogen, produced via biotechnological or chemical processes may become feasible as fuel sources. Limitations in quantity are caused by net productivities of photosynthesis, which are limited by several factors, e.g., by the supply of water, limited availability of land, and conversion losses. As a consequence, biofuels as they exist can only contribute to a limited extent to securing raw material supplies for energy requirements in the future. Efficiency improvements in processing technologies and changes in consumer behavior and attitude will also be required.