The activity coefficients at infinite dilution, gamma(infinity)(13) for 32 solutes: alkanes, alkenes, alkynes, cycloalkanes, aromatic hydrocarbons, alcohols, thiophene, tetrahydrofurane, tert-butyl methyl ether, and water in the ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate [BMIM][CF3SO3] were determined by gas-liquid chromatography at the temperatures from 298.15 to 368.15 K. The partial molar excess enthalpies at infinite,3 values obtained over the temperature range. dilution values Delta H-1(E infinity) were calculated from the experimental gamma(infinity)(13) The selectivities for the hexane/benzene, cyclohexane/benzene, n-hexane/thiophene, n-decane/thiophene, cyclohexane/thiophene, toluene/thiophene, and oct-l-ene/thiophene separation problems were calculated from the gamma(infinity)(13). Obtained values were compared to the literature values for the other ionic liquids, NMP, and sulfolane.