Ionic liquids, with their very low vapor pressures and unique solvent properties, are potentially useful solvents for separating organic liquid mixtures by solvent extraction or by extractive distillation. In this work, the activity coefficients at infinite dilution, gamma(13)(infinity), for both polar and nonpolar solutes in the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate have been determined by gas-liquid chromatography at the temperatures (298.15, 313.15, 323.15) K. The partial molar excess enthalpies at infinite dilution and the selectivity values were calculated from the gamma(13)(infinity), values obtained over the temperature range. The selectivity values have been determined and are used to predict the solvent potential of the ionic liquid for the separation of liquid mixtures by extractive distillation.