The activity coefficients at infinite dilution, gamma(infinity)(13) for 32 solutes: alkanes, alkenes, alkynes, cycloalkanes, aromatic hydrocarbons, alcohols, thiophene, tetrahydrofuran, tert-butyl methyl ether, and water in the ionic liquid triethylsulphonium bis(trifluoromethylsulfonyl)imide [Et3S][NTf2] were determined by gas-liquid chromatography at the temperatures from T = 298.15 K to T = 368.15 K. The partial molar excess enthalpies at infinite dilution values Delta H-1(E,infinity) were calculated from the experimental gamma(infinity)(13) values obtained over the temperature range. The selectivities for the n-hexane/benzene and cyclohexane/benzene, n-hexane/thiophene, cyclohexane/tiophene, benzene/tiophene, and hexen-1-ene/n-hexane separation problems were calculated from the gamma(infinity)(13) and compared to the literature values for other ionic liquids, NMP, and sulfolane. (C) 2008 Elsevier Ltd. All rights reserved.