Biofuels have received considerable attention as a more sustainable solution for transportation fuels. Used vegetable oil, normally considered a waste product, has been suggested as a possible candidate. Herein we perform a life cycle assessment to determine the environmental impact of biodiesel fuel produced from waste vegetable oil. We present a cradle to fuel model that includes the following unit processes: growing and harvesting, soy oil processing, cooking, waste vegetable oil refining, transesterification to produce biodiesel fuel and transportation when required. For growing and harvesting, national historical data for yields, energy required for machinery, fertilizers (nitrogen, phosphorous and potassium), herbicides, pesticides and nitrous oxide production are considered. In soy oil processing, crushing and extraction using hexane are included. For cooking, typical fryer performance and food production are considered. In order to determine a mass balance for the cooking operation, oil carryout and waste oil removal are estimated. During waste oil refining, oil is filtered and water removed. Methanol and a catalyst are used in the process of transesterification with glycerin as a byproduct. Transportation is considered using diesel trucks. Data from GREET is used throughout to compute global warming potential (GWP) and energy consumption in terms of cumulative energy demand (CED). Mass allocation is applied to the soy meal produced in refining, oil utilized for cooking and glycerin produced during transesterification. Results are compared to traditional diesel fuel and gasoline. Individual processes are examined to determine possibilities for reduction of GWP and CED. Suggestions are made for improvements in environmental impact using alternative or more efficient methods. The study should provide useful information on the sustainability of biodiesel fuel produced from waste cooking oil.