The activity coefficients at infinite dilution, gamma(infinity)(13), for 44 solutes, including alkanes, cycloalkanes, alkenes, allcynes, aromatic hydrocarbons, alcohols, water, thiophene, tetrahydrofuran, ethers, and ketones in the ionic liquid (IL) N-hexyl-3-methylpyridinium tosylate (p-toluenesulfonate), [HM(3)Py] [TOS], were determined by gas-liquid chromatography at temperatures from 338.15 to 368.15 K. The densities of [HM(3)Py][TOS] as a function of temperature have been measured at temperatures higher than the melting temperature and were extrapolated to T = 298.15 K. The gas-liquid partition coefficients, K(L) were calculated for all solutes. The partial molar excess Gibbs energies Delta G(1)(E,infinity), enthalpies Delta H(1)(E,infinity), and entropies Delta S(1)(E,infinity) at infinite dilution were calculated from the experimental gamma(infinity)(13) values obtained over the temperature range. The selectivities for different separation problems including n-heptane/benzene, cyclohexane/benzene, and n-heptane/thiophene were calculated from gamma(infinity)(13) and compared to literature values for tosylate-based ILs, or hexyl-substituted cations of ILs, or pyridynium-based IL, or N-methyl-2-pyrrolidinone (NMP), and sulfolane.