Our earlier study on nonaqueous liquid mixture system (triglycerides and oleic acid) showed that the contribution of solution-diffusion to transport in nonporous (dense) membranes is more than usually observed in reverse osmosis membranes. Triglycerides and oleic acid were independently studied in the present study. The results showed that pressure had significant effect on the permeation rates. The behaviour of pure systems was similar to triglycerides-oleic acid mixture. In the present study on triglycerides-tocopherols model system, tocopherols preferentially permeated through nonporous membranes. Increased concentration of tocopherols increased the feed viscosity, however, the total permeate flux remained practically constant. Whereas in triglycerides-oleic acid mixture system, increased concentration of oleic acid reduced the feed viscosity and increased the total flux. The comparative performance of these two different systems revealed that viscosity does not play significant role in the permeation. Further, the analysis establishes that dense membrane theory could qualitatively explain the differential permeability of oil constituents. (C) 2003 Elsevier Ltd. All rights reserved.