This work is part of an investigation to determine activity coefficients at infinite dilution gamma(13)(infinity) of hydrocarbons in the industrially important polar solvent tetrahydrothiophene-1,1-dioxide (sulpholane), by medium pressure gas liquid chromatography (g.l.c.). In this work the activity coefficients at infinite dilution for a series of 1-alkenes (C-6 to C-8), 1-alkynes (C-6 to C-8), and cycloalkanes (C-7 and Ca) have been measured in the polar solvent sulpholane at T = 303.15 K and T = 313.15 K. The activity coefficients of some of the solutes discussed in this work would be difficult to determine by any other method because of their low solubility in sulpholane. The mixed second virial coefficients used in this work were determined by assuming the principle of corresponding states, the Hudson and McCoubrey combining rules for T-c,T-12, the Lorentz rule for V-c,V-12, and the McGlashan-Potter equation.