Soybean and rapeseed oils were epoxidized 6 h/75degreesC in benzene as solvent over a macroporous Amberlyst-15 with peracetic acid prepared in situ. The viscosity indices of the epoxidates were slightly inferior to those of the original oils but superior to those of mineral oils. Superior were also the maximum non-seizing load, load-wear index, seizure load, and limiting seizure pressure. Lubrifiers like Tiolan R-10 (rapeseed off sulfurized to contain 10% S) enhanced several times the limiting seizure pressure. Resistance to oxidation rose, but was still lower than that of mineral oils. Butyrohydroxytoluene (BHT), 0.25%, caused essential improvement Methanolysis and transesterification with 2-ethylhexanol enhanced the solubility in mineral oil so that semisynthetic oils could be made containing 25 or 50% of the esterificate.