Edible oil processing has become one of the prime targets for membrane applications. In the present study, attempts were made for the first time to examine the applicability of the transport equations for oil systems. Permeability of the constituents of the homogeneous mixtures and rejections of individual constituents were studied, Oleic acid permeated preferentially when compared with triglycerides. The total permeate flux increased from 90.6 to 151g/(m(2) h) when the oleic acid content in the feed was increased from 1.9 to 21.2%, which is mainly due to the increase in the permeation rate of oleic acid. The synergistic effect of preferential sorption and concentration dependent solubility as well as diffusivity could be responsible for the higher relative permeability of oleic acid. In the present case of processing liquid mixtures (oleic acid and triglycerides) by nonporous denser membranes, the contribution of solution-diffusion to transport is more than usually observed in reverse osmosis (RO) membranes. Higher operating temperature and pressure increased the total permeate flux. Relative permeation rate of oleic acid increased with pressure. In case of phosphatidylcholine (PC) and triglycerides (solute-solvent) system, the rejection of PC was above 98% and it did not vary significantly either with feed concentration or with operating conditions. The membrane rejected chlorophyll almost completely.