Transesterification between ethyl oleate and glycerol, or esterification between oleic acid and glycerine by the immobilized lipase preparation SP 435 from Candida antarctica, was investigated. Different temperatures and reactants ratios were tried. In all cases, transesterification yielded better results. When the reaction was carried out in n-heptane the addition of 3% water gave highest yields to mono and diolein; the formation of diolein can reach levels comparable to those of monoolein. However, when the reaction was carried out in one-liquid-phase only (in the presence of acetonitrile or acetone), the reaction was much more selective to monoolein.