The mass fraction activity coefficients at infinite dilution, Omega(infinity)(13), for 20 different solutes: alkanes (C-6-C-9), alkenes (C-6, C-7), alkynes (C-6, C-7), cycloalkanes (C-6, C-7), aromatic hydrocarbons (benzene, toluene, thiophene), alcohols (C-1-C-3), ethers (diethyl ether, dipropyl ether, tetrahydrofuran), and propanone were measured in the commercially available dendritic polymer PAMAM-C-12 generation number 3, by inverse gas chromatography (IGC), at the temperatures from (298.15 to 318.15) K. The partial mass excess enthalpies of mixing at infinite dilution Delta H-1(E,infinity) were calculated from the experimental Omega(infinity)(13) values over the temperature range. The selectivity for different separation problems was calculated from Omega(infinity)(13) and compared to the literature values for the other polymers.