Ethanol derived from bacterial fermentation is a potential alternative fuel source. Ethanol resistant FBR5 mutants were isolated by subjecting independent cultures to multiple passages of alcohol challenges. Mutants were isolated from normal aerobic spread plates and from the anaerobic regions of pour plates. Pilot fermentations were conducted under anaerobic conditions at 30°C in LB media supplemented with 120 g/L xylose. One aerobic mutant strain produced ∼ 20% more ethanol than the parent FBR5 strain. The highest ethanol yields were obtained with an anaerobic mutant strain, which produced 60% more ethanol than the parent. Fermentation results under optimized conditions and ethanol yields of additional mutants were discussed. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 10/30/2005-11/4/2005).