This study investigates the resource availability, energetic efficiency, and economic feasibility of converting edible and inedible beef tallow into biodiesel, a substitute diesel fuel. A resource assessment of edible and inedible beef tallow generation in the United States was performed for the period of 1997-2001. At that time, an average of more than 1.8 Mt (4 billion pounds) of edible and inedible tallow were generated each year in the 11 largest commercial cattle slaughtering states, which would equate to more than 2.08 GL (551 million gallons) of biodiesel (similar to 1% of the total US distillate consumption). Tallow is a by-product of our meat production and processing system, which complicates its energy and economic analysis. Although tallow is available in significant quantities at relatively low cost, it is not intentionally produced as a feedstock for biodiesel. Because of this uncertainty, energetic (energy ratio) and economic (production cost per gallon) feasibilities were estimated for three different system boundaries: (1) conversion of tallow by a continuous-flow transesterification process only with co-product (glycerin) credit, (2) rendering plant operations plus tallow transesterification, and (3) growth and maintenance of the beef animal from conception through rendering and transesterification. Energy ratios varied from 17.29 to 0.81 within the three system boundaries based on various assignments of the co-product energy credit for glycerin. Cost-sensitivity analyses were performed to determine the effect of feedstock cost and by-product (glycerin) credit on biodiesel cost. Feedstock cost had the greatest impact, while by-product credit effect was minimal. Cost of production ranged from $0.22 to $0.63 L-1 ($0.82-$2.38 gallon(-1)) produced. (c) 2006 Published by Elsevier Ltd.