The method recently developed by our group for the determination of activity coefficients at infinite dilution by g.l.c., for systems involving moderately volatile solvents, is used in this work to determine the activity coefficients for the solutes : pentane, hexane, heptane, cyclopentane, cyclohexane, and benzene in the solvent : dodecane, at the temperatures 280.15 K and 298.15 K. All known activity coefficients at infinite dilution for the above solutes in n-alkane solvents ranging from CH3(CH2)(3)CH3 to CH3(CH2)(34)CH3 have been summarized in graphical form and are compared with the experimental results obtained in this work.