Approximately 50% of the oil used in the United States is imported, two-thirds of which is used to power transportation vehicles. This translates to the consumption of ~8.5 million barrels of gasoline daily. With this consumption comes significant pollution of our atmosphere, water and soil. This dependence of foreign oil and significant resulting pollution have led to a series of laws and policies aimed at introducing alternative fuels for passenger cars and light trucks. Although the 1988 Alternative Motor Fuels Act required a comprehensive study of the environmental and public health issues associated with fuel alternatives, no truly comprehensive evaluation of the life cycle environmental impacts of different transportation fuel options has been attempted to date. The most notable example of the failure of these laws and related regulations to adequately protect the environment is the widespread contamination of ground and surface waters by methyl tert-butyl ether (MTBE). The objectives of this seminar will be to critically review our present state-of-knowledge about the environmental impacts of alternative fuels and to define the gaps in our knowledge and assessment techniques that currently limit the usefulness of this knowledge in policy decisions. Following a general introduction of the life cycle for a few example fuels, the presentation will focus on the energy value of fuel grade ethanol to illustrate the difficulties in understanding the lifecycle impacts from fuel use. Although this fuel has been used and studied for decades, differences in the data and assessment tools used have resulted in significant variability and uncertainty in estimates of the energy required to produce this fuel. The seminar will conclude with recommendations for an analysis framework required to improve our understanding of the environmental impacts of alternative fuels and the usefulness of this knowledge for decision makers.