The activity coefficients at infinite dilution, gamma(infinity)(13), for hydrocarbon solutes, alcohols, water, thiophene, ethers, and ketones in the ionic liquid 1-butyl-3-methylimidazolium tosylate (p-toluenesulfonate), [BMIM][TOS], have been determined by gas liquid chromatography at temperatures T = (338.15, 348.15, 358.15, and 368.15) K. The selectivity values have been calculated at T = 338.15 K, and the results indicate that the ionic liquid [BMIM][TOS] should be considered as a solvent for separation of aromatic sulfur compounds from alkanes. 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 earlier by us and from the literature.