Activity coefficients at infinite dilution (gamma(infinity)(i)) for organic solutes: alkanes, alkenes, and alkyl benzenes in two ionic liquids (ILs) 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) and 1-ethyl-3-methylimidazolium dimethylphosphate ([EMIM][DMP]) have been measured by the gas-liquid chromatographic method (GLC). The measurements were carried out in the temperature range of (313.15 to 363.15) K. The values of the partial molar excess enthalpies at infinite dilution ((H) over bar (E,infinity)(i)) were derived from the temperature dependence of the gamma(infinity)(i) values. The entropies (T-ref(S) over bar (E,infinity)(i)) and Gibbs energies ((G) over bar (E,infinity)(i)) of organic solutes at a reference temperature T-ref = 298.15 K were also calculated from the gamma(infinity)(i) values. Selectivity (S-ij(infinity)) and capacity (k(j)(infinity)) at infinite dilution at T = 323.15 K have been determined for hexane (i)/benzene (j), cyclohexane (i)/benzene (j). The results were analyzed in comparison to literature data for other ILs with the [MMIM] and [EMIM] cations. For three isomeric xylenes separation problems, selectivity at T = 323.15 K were also obtained from the gamma(infinity)(i) values. (C) 2015 Elsevier Ltd. All rights reserved.