The activity coefficients at infinite dilution, for various solutes: alkanes, cycloalkanes, 1-alkenes, 1-alkynes, benzene, alkylbenzenes, and alcohols in the ionic liquids 1-butyl-3-methylimidazolium bis(oxalato)borate [BMIM][BOB] and 1-hexyl-3-methyl-imidazolium bis(oxalato)borate [HMIM][BOB] have been determined by gas-liquid chromatography at the temperatures ranging from 308 to 348K. The partial molar excess enthalpies at infinite dilution H-i(E infinity) of the solutes in the ionic liquids were also derived from the temperature dependence of the gamma(infinity)(i) values. The selectivities for the hexane/benzene, cyclohexane/benzene and hexane/hexene separation problems were calculated from experimental infinite dilution activity coefficient values and compared to the other ionic liquids, taken from the recent literatures. (C) 2010 Elsevier B.V. All rights reserved.