In this paper, the transesterification of soybean oil with ethanol is studied. The transesterification process can be affected by differing parameters. The biodiesel production process was optimized by the application of factorial design 2(4) and response surface methodology. The combined effects of temperature, catalyst concentration, reaction time and molar ratio of alcohol in relation to oil were investigated and optimized using response surface methodology. Optimum conditions for the production of ethyl esters were the following: mild temperature at 56.7 degrees C, reaction time in 80 min, molar ratio at 9:1 and catalyst concentration of 1.3 M. (C) 2010 Elsevier B.V. All rights reserved.