Activity coefficients at infinite dilution gamma(infinity)(12) were determined for organic solutes in two ionic liquids 1-ethyl-3-methylimidazolium methylphosphonate [EMIM][(MeO)(H)PO2] and 1.3-dimethylimidazolium methylphosphonate [DMIM][(MeO)(H)PO2] by gas-liquid chromatography at temperatures within the range (313.15 to 373.15) K. The values of the selectivity and capacity for few separation problems cyclohexane/benzene, cyclohexane/thiophene and cyclohexane/pyridine were calculated from activity coefficients at infinite dilution data and compared to literature values for other ionic liquids and some industrial solvents such as sulfolane, N-methyl-2-pyrrolidone (NMP) and N-formylmorpholine (NFM). The selectivity values of both ILs investigated in this study are greater than that for NMP, NFM, and sulfolane. These results indicate the potential use of the two ILs in extractive separation processes. (C) 2015 Elsevier Ltd. All rights reserved.