The permeability of various organic solvents through a composite dense nonporous membrane comprising a silicon polymer as the active layer was studied to elucidate the transport mechanism under steady-state conditions. The permeability was calculated from the difference in the parameters of the solvent and the membrane polymer, vertical bar delta(1) - delta(2)vertical bar, and the molecular weight (size) of the solvent, M-2; vertical bar delta(1)-delta(2)vertical bar and M-2 would correspond to the solubility and diffusivity, respectively. Generally, the permeability of the different groups of common solvents classified on the bases of their molecular sizes tended to increase with a decrease in vertical bar delta(1) - delta(2)vertical bar. However, the M-2 values of the alkane solvents were inversely proportional to their permeabilities. For a more detailed analysis of the transport mechanism, the regular solution model was used. The permeate flux of the solvent, ln (J(2)), showed a linear dependence on the mole fraction of the solvent in the membrane phase, ln (X-2), and the square of the volume fraction of the solvent in the membrane polymer phase (degree of swelling), Phi(2)(2). In the case of the common solvents, ln (J(2)) showed a linear dependence on the product of the molar volume of the solvent (V-2) and the square of the solubility parameter difference (delta(1) - delta(2))(2) at constant pressure and temperature. In the case of the alkane solvents, a good correlation was observed between ln (J(2)) and V-2, as the (delta(1)-delta(2))(2) values were numerically around unity. These results agreed with the conclusions drawn from studies performed using the solution-diffusion model. Thus, this new approach is expected to help in the accurate elucidates of the mechanism of transport of a non aqueous liquid through a composite dense nonporous membrane.