Activity coefficients at infinite dilution gamma(infinity)(i) of 46 solutes such as alkanes, alkenes, alkylbenzenes, linear and branched C-1-C-6 alcohols, esters, aldehydes, cyclohexanone oxime, and epsilon-caprolactam in the ionic liquid (IL) 1-ethyl-3-methylimidazolium ethyl sulfate or [EMIM][EtSO4] have been determined by gas chromatography using the IL as the stationary phase. The measurements were carried out at different temperatures between (302 and 396) K. From the temperature dependence of the limiting activity coefficients, partial molar excess enthalpies at infinite dilution H-i(E,)infinity of the solutes in the ILs have been derived. Vapor-liquid equilibria (VLE) of binary mixtures containing water with [EMIM][EtSO4] were studied using the transpiration method. VLE measurements were carried out over the broad concentration range at temperatures between (302.9 and 322.9) K. Activity coefficients gamma(i) of water in the [EMIM][EtSO4] have been determined from the VLE data and are described formally by using the NRTL equation. Furthermore, activity coefficients in infinity dilution gamma(infinity)(i) of water in the IL [EMIM][ EtSO4] have been derived by extrapolation to the infinite dilution of water.