The capillary-column inverse gas chromatography (CCIGC) method was used to determine diffusivity data for several solvents in poly(styrene) at conditions approaching infinite dilution of the volatile component. Measurements were made over a temperature range traversing the polymer glass transition temperature. The chromatographic data were analyzed by employing the elution model developed by Pawlisch et al. The Vrentas-Duda free-volume theory of diffusion was utilized to correlate the diffusion data and to interpret the effect of the glass transition temperature on the diffusion coefficient and on the effective activation energy in the limit of zero penetrant concentration. The free-volume theory was found to correlate the diffusion data very well. The results of this study confirmed the free-volume concept that molecular diffusion is not as inhibited as one might expect below the glass transition temperature of the polymer.