Experimental flux and selectivity results are shown for the toluene-water-silicone rubber system in a tubular transverse flow module. These results are compared to predictions offered from nonlinear pervaporation models based upon modified Flory-Huggins and Lattice Fluid thermodynamics. A comparison of experimental with model results shows good predictions of solute flux for both thermodynamic theories. However, the model was discovered to be very sensitive to calculations of infinite dilution diffusion coefficients and a priori predictions of experimental membrane selectivities were underestimated.