Response surface methodology (RSM) based on central composite rotatable design (CCRD) was used to optimize the three important reaction variables-methanol quantity (M), acid concentration (C) and reaction time (T) for reduction of free fatty acid (FFA) content of the oil to around 1 % as compared to methanol quantity (AT) and reaction time (T) and for carrying out transesterification of the pretreated oil. Using RSM, quadratic polynomial equations were obtained for predicting acid value and transesterification. Verification experiments confirmed the validity of both the predicted models. The optimum combination for reducing the FFA of Jatropha curcas oil from 14% to less than 1% was found to be 1.43% v/v H2SO4 acid catalyst, 0.28 v/v methanol-to-oil ratio and 88-min reaction time at a reaction temperature of 60 degrees C as compared to 0.16 v/v methanol-to-pretreated oil ratio and 24 min of reaction time at a reaction temperature of 60 degrees C for producing biodiesel. This process gave an average yield of biodiesel more than 99%. The fuel properties of jatropha biodiesel so obtained were found to be comparable to those of diesel and confirming to the American and European standards. (c) 2007 Elsevier Ltd. All rights reserved.