Citric acid production was maximized by Yarrowia lipolytica NCIM 3589 in submerged fermentation using byproduct glycerol obtained during biodiesel production, which is produced by the transesterification of oils obtained from the seeds of nonedible plants as the renewable carbon source. Response surface methodology (RSM) involving Doehlert experimental design was adopted to evaluate the amount of citric acid produced by most important factors, such as yeast extract, raw glycerol, and salt solution concentration. Besides reducing the number of experiments required for optimization, this technique allowed to quantify the amount of citric acid in any part of the experimental domain. The optimal set of conditions for maximum citric acid production was as follows: yeast extract 0.2682 g/l, raw glycerol 54.4081 g/l, and salt solution concentration 13.6936% (v/v). A maximum citric acid concentration of 77.3999 g/l was obtained at these optimal conditions. (c) 2006 Elsevier Inc. All rights reserved.