Federal standards that mandate improved fuel economy have resulted in the increased use of lightweight materials in automotive applications. However, the environmental burdens associated with a product extend well beyond the use phase. Life cycle assessment is the science of determining the environmental burdens associated with the entire life cycle of a given product from cradle-to-grave. This report documents the environmental burdens associated with every phase of the life cycle of two fuel tanks utilized in full-sized 1996 GM vans. These vans are manufactured in two configurations, one which utilizes a steel fuel tank, and the other a multi-layered plastic fuel tank consisting primarily of high density polyethylene (HDPE). This study was a collaborative effort between GM and the University of Michigan's National Pollution Prevention Center, which received funding from EPA's National Risk Management Research Laboratory. Findings from this study include: Material production phase solid waste production for steel greatly exceeds that for HDPE, however, material production phase energy consumption is much higher for HDPE than steel. The use phase dominates the consumption of energy, the gas phase emissions of CO, CO2, NOx, and HC, and the generation of liquid phase dissolved solids. In each of these categories, the HDPE system is environmentally advantageous over the steel system. The manufacturing phase contributes the largest fractions of airborne particulate matter, liquid phase suspended solids, waterborne oil and grease, and waterborne metals. In each of these, except waterborne metals, the HDPE system is environmentally advantageous over the steel system. The end-of-life phase dominates the generation of solid waste. In this category, the steel system is environmentally advantageous over HDPE. This conclusion assumes there is no recycling of the HDPE system.