The measurements of the diffusion coefficients of trace amounts of three solvents, benzene, toluene, and ethylbenzene, in polyisobutylene (PIB) were performed at elevated temperatures by inverse gas chromatography. A packed chromatographic column was used. The Hadj-Romdhane-Danner mathematical model to describe the chromatographic process and the corresponding moment analysis were adopted to determine the diffusion coefficients. The goodness of fit of the experimental diffusion coefficient data to the Vrentas-Duda free-volume relationship indicates that the free-volume theory is a very good description of the relationship of the observed solvent diffusion coefficient with temperature. Furthermore, the solvent diffusivity data were compared, by using the free-volume theory, with those determined by nuclear magnetic resonance method for the systems of PIE/benzene and PIB/ toluene. The good agreements show that these diffusivity data obtained by inverse gas chromatography measurement are reliable.