Activity coefficients at infinite dilution, gamma(similar to)(13), for 32 organic compounds: alkanes, alk-1-enes, alk-1-ynes, cycloalkanes, aromatic hydrocarbons, alcohols. thiophene, tetrahydrofuran, tert-butyl methyl ether and water in the ionic liquid 1-butyl-1-methylpyrrolidinium trifluromethanesulfonate [BMPYR][CF3SO3] were determined by gas-liquid chromatography at the temperatures ranging from 298.15 to 368.15 K. The partial molar excess enthalpies at infinite dilution Delta H-1(E similar to) were calculated from the experimental gamma(similar to)(13) values obtained over the temperature range. The selectivities for the n-hexane/benzene. cyclohexane/benzene, n-hexane/thiopliene, cyclohexane/thiophene, benzene/thiophene and hexen-1-ene/n-hexane separation problems were calculated from the gamma(similar to)(13) and compared to the literature values for other ionic liquids, NMP and sulfolane. (C) 2009 Published by Elsevier B.V.