The transesterification of soybean oil with methanol was studied using solid acid catalysts, at 60 degrees C and atmospheric pressure. Nafion membranes, ion-exchange resins and poly(vinyl alcohol) membranes containing sulfortic groups were used as catalysts for the transesterification reaction studied. The reactions were carried out in a three-necked reactor using all the catalysts in the form of pellets. Nafion and PVA membranes in the form of film were also used in a membrane reactor. The PVA membrane modified with sulfossucinic acid was, in both cases, the most active catalyst. The concentration profiles obtained with the catalysts in the form of pellets exhibited an initial induction period, which disappears when the reaction is performed in the membrane reactor. (c) 2006 Elsevier B.V. All rights reserved.