Biodiesel production via transesterification of rapeseed oil in supercritical methanol was performed without catalysts. Response surface methodology (RSM) was used to evaluate the relationships between the content of fatty acid methyl esters (FAMEs) and reaction parameters, such as reaction temperature, reaction pressure, reaction time, and the molar ratio of methanol to oil. A central composite design was employed to fit the available response data to a second order polynomial RS model. The optimal conditions maximizing the content of FAMEs in the biodiesel were investigated. Results showed that the optimum processing conditions were 330 C. 210 bar, a reaction time of 16 min, and a molar ratio of methanol to oil of 50 mol/mol. The predicted response value for these conditions was 93.6% methyl esters and it was in agreement with the experimental value. (C) 2012 Elsevier B.V. All rights reserved.