The alkaline-catalyzed ethanolysis of rapeseed oil was studied. In the case of homogeneous catalysis (KOH), the effects of various reaction conditions on the quantity and quality of biodiesel (yield, purity, acid number, carbon residue, free glycerol, potassium content) and the glycerol phase (weight, soaps and ethyl esters content) were studied. The studied reaction conditions were: the reaction temperature and time, the catalyst concentration, the molar ratio of ethanol to oil, the revolutions of stirring, the temperature and time of deethanolisation and the initial temperature of the separation. Data was evaluated by linear regression on the statistical basis of multivariable systems. The final linear models were verified by independent experiments and they are able to predict the biodiesel quantity and quality in the range of the reaction conditions. Finally, the factor analysis of the ester phase variables was carried out. Moreover, ethanolysis was catalyzed by a heterogeneous catalytic system; attention was focused not only on catalyst activity but also on catalyst stability, which was determined by potassium leaching. (C) 2012 Elsevier Ltd. All rights reserved.