The activity coefficients at infinite dilution, gamma(infinity)(13), for hydrocarbon solutes and some alcohols in the ionic liquid trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide [3C(6)C(14)P][Tf(2)N] have been determined by gas-liquid chromatography at temperatures T = (303.15, 308.15, 313.15, and 318.15) K. The selectivity values have been calculated at T = 308.15 K, and the results indicate that the ionic liquid [3C(6)C(14)P][Tf(2)N] should not be considered as a solvent for separation of alkanes and aromatics. The partial molar excess enthalpy values at infinite dilution Delta H(1)(E infinity), determined in this work, together with the values gamma(infinity)(13) have been discussed in terms of intermolecular interactions and compared to results of related. systems obtained from the literature.