Fatty acid methyl esters synthesis from crude Jatropha oil using an ultrasound-assisted process was investigated. Several gamma alumina (Al) supported tungstophosphoric acid (TPA) catalysts were synthesized and characterized to elucidate their catalytic behaviors. TPA loadings on the support between 15% and 35% were investigated. The catalyst with 25% loading achieved the highest yield of 64.3% in 60 min. Effects of reaction time (10-50 min), reaction molar ratio (5:1-25:1), ultrasonic amplitude (30-90% of the maximum sonifier power) and catalyst amount (2.5-4.5 w/w oil) were investigated and optimized. Mathematical representation of FAME yield was successfully generated and statistically validated. A highest reaction yield of 84% was achieved under the optimum conditions i.e. at an ultrasonic amplitude of similar to 60%, a molar ratio of 19:1 and a reaction temperature of 65 degrees C in just 50 min. Interactions between the reaction variables were also statistically validated. The catalyst was also investigated for possible reusability. (C) 2013 Elsevier Ltd. All rights reserved.