The enzymatic esterification of fatty acids (mainly oleic acid) and ethanol is studied in this work. The reactions are catalyzed by commercial immobilized lipases from Candida antarctica (Novozyme, 435) and are carried out in a batch reactor at solvent free conditions. The influence of several important reactions conditions as temperature, initial molar ratio, initial water percentage, and enzyme percentage on the equilibrium conversion and the initial reaction rates is carefully analyzed. A non-linear relationship is established between the initial reaction rates and the enzyme percentage. An optimum value of the initial molar ratio is detected for each enzyme percentage and the effect of inhibition by alcohol is confirmed. Under the studied conditions, it is demonstrated that the influence of the external mass transfer resistance on the reaction rate is not significant. Therefore, the experimental data are appropriated for kinetic modeling purposes. (c) 2006 Elsevier Inc. All rights reserved.