The reaction mechanism involved in the alkaline-catalyzed transesterification of pentylic acid triglyceride is studied employing Density Functional Theory (DFT). DFT calculations for both the gas phase and in solution indicate a stepwise mechanism for each of the three steps of the reaction. The formation of the tetrahedral intermediate adduct is the rate determining step of each transesterification reaction. The activation energies of each step in the solution phase are higher than those of the gas phase. The activation energies obtained for the tri, di and monoglyceride transesterifications are in good agreement with experimental measurements. Three different pathways are considered and DFT calculations indicate the transesterification of the middle ester bond (C-2) followed by the subsequent transesterification of the outside ester bonds (C-1 and C-3) with lower activation energy. (c) 2012 Elsevier Ltd. All rights reserved.