The transesterification of various triglycerides was considered in terms of the activation energy obtained from quantum computational chemistry. According to these values, the effect upon the reactivity of the structure of the triglyceride is not particularly large. Moreover, the transesterification reaction is completed via a transition state, in which ring formation consisting of the carbon of the carboxyl and alkoxy groups appears, even if a long-chain alcohol is used as a reactant. Finally, an ideal reaction pathway, in which the ester bond at the center of the triglyceride is transesterified before peripheral ester bonds, was shown by an activation energy analysis and electrostatic potential (ESP) distribution. (c) 2008 Published by Elsevier Ltd.