The inverse gas chromatography technique was applied to measure solubility and diffusivity in a ternary polymer-solvent-solvent system. This method requires the comparison of the experimental elution profiles with theoretically predicted ones. A new simplified model was developed to describe ternary systems. In addition, a new experimental apparatus was constructed to monitor the independent composition profiles during a multicomponent experiment. The model was evaluated using experimental data for the system poly(vinyl acetate)-toluene-tetrahydrofuran at 80 and 100 degrees C. Solubility and diffusivity of the mixed solvents in poly(vinyl acetate) were collected at 80 degrees.