The feasibility of enzymatic thioesterification between oleic acid and butanethiol in n-hexane, with the immobilised lipase (Lipozyme) from Mucor miehei, has been demonstrated. The immobilised enzyme quantity (100 mg), temperature (40 degrees C), pH range (6-9) and water content (10%) were studied and their optimum values were determined. A preliminary kinetic study indicated a low butanethiol affinity for the enzyme (K-m = 1 . 85 mol dm(-3)). Even when butanethiol was used without solvent, no substrate inhibition was observed. The possibility of carrying out this reaction in a natural solvent, supercritical carbon dioxide (SCCO2), was successfully verified. After 8 h reaction, a conversion yield of oleic acid of about 33% was obtained.