The present work is part of an investigation extending the determination of activity coefficients lambda(13)(infinity) at infinite dilution by medium-pressure g.l.c. to include Volatile and polar solvents. The activity coefficient at infinite dilution for a series of n-alkane solutes (C-5 to C-7), cycloalkanes (C-5 and C-6), benzene, tetrahydropyran, and tetrahydrofuran have been measured in a polar solvent : tetrahydrothiophene-1, 1-dioxide (sulfolane) at the temperature 303.15 K. The effects of the size of the injection volumes of the solute and the solvent loading on the column were investigated in order to ensure infinite dilution and non-adsorption conditions, respectively. The mixed second virial coefficients used in this work were calculated by assuming the principle of corresponding states, the Hudson and McCoubrey combining rules, and the McGlashan and Potter equation of state. A modified NRTL equation was used to determine gamma(13)(infinity) for benzene in sulfolane from finite-mole-fraction results. The gamma(13infinity) results obtained here highlight the polar nature of sulfolane.