The preesterification of free fatty acid (FFA) containing vegetable oils by strong acid ion-exchange resins was studied. The catalysts were characterized by scanning electron microscopy (SEM) and ion-exchange capacity. Based on a simple kinetic model the rate constants were determined. The effect of the catalyst structure, particle size, stirring speed, oil properties and water removal method on the reaction rate was investigated. Calculation of the turn over frequencies (TOFs) revealed high catalyst activities. Excellent conversions were obtained even without water removal, due to an extractive esterification. During recycling durability tests a catalyst activity loss occurred. The deactivation mechanism was investigated and the exhausted catalysts were successfully regenerated. A catalyst fouling was not observed. The presented preesterification process facilitates the processing of low quality, high FFA containing oils to biodiesel via basic transesterification and might help to reduce the production costs. (C) 2009 Elsevier B.V. All rights reserved.