The activity coefficients at infinite dilution, gamma(infinity)(13), for 37 solutes: alkalies, alkenes, alkynes, cycloalkanes, aromatic hydrocarbons, alcohols, thiophene, ethers, ketones, and water in the ionic liquid 1-butyl-3-methylpyridinium trifluoromethanesulfonate [1,3bmPY][CF(3)SO(3)] were determined by gas-liquid chromatography at the temperatures from (308.15 to 358.15) 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 aliphatic/aromatic hydrocarbon separation problem were calculated from gamma(infinity)(13) and compared to the literature values for other ionic liquids, N-methylpyrrolidone and sulfolane.