Modern transportation almost exclusively depends on fossil fuels, mainly petroleum-based fuels such as gasoline, jet fuel, diesel, liquefied petroleum gas, and natural gas. Of particular concern are the liquid fuels used in cars, airplanes, and trucks because of the combination of rising oil prices, exhaustion of crude oil reserves, energy insecurity, climate change, and environmental pollution. These concerns have spurred research and development interests in biofuels (ethanol, higher alcohols, biodiesel, biogas, and Fisher-Tropsh liquids) from a variety of biomass. The world is on the verge of an unparalleled increase in the production and use of biofuels for transportation. First generation biofuels, namely grain-based ethanol and vegetable-oil-based biodiesel, have faced difficulties due to competition with food supplies, life cycle and energy balance assessments, and costs. One of the main research directions in biofuels, therefore, is the production of fuels from non-food resources such as algal and lignocellulosic biomass. Such biofuels would provide a ''greener'' alternative to fossil fuel energy because they are renewable, carbon neutral, and available in one form or another throughout the world.