Vapor-liquid equilibria (VLE) for the binary systems methylcyclohexane-toluene and 1-octene-n-octane and the ternary systems with the ionic liquid 1-hexyl-3-methyl-imidazolium bis(trifluoro-methylsulfonyl)imide [HMIM](+)[BTI](-) as entrainer were measured. The addition of the ionic liquid leads to an increase of the separation factors. Excess enthalpies (HI) were measured for methylcyclohexane and n-octane in the same ionic liquid as well. Furthermore activity coefficients at infinite dilution (gamma(infinity)) were determined for a few solutes in various ionic liquids such as 1-hexyl-3-methyl-imidazolium bis(trifluoro-methylsulfonyl)imide [HMIM](+)[BTI](-), 1-hexyl-3-methyl-imidazolium trifluoro-methanesulfonate [HMIM](+)[OTF](-), 1-methyl-1-octyl-pyrrolidinium bis(trifluoromethyl-sulfonyl)imide [MOPYR](+)[BTI](-), 1-methyl-l-butyl-pyrrolidinium trifluoromethanesulfonate [MBPYR](+) [OTF](-) and 1-ethyl-3-methyl-imidazolium ethyl sulfate [EMIM](+)[EtOSO3](-). The gamma(infinity)-values were used to determine the selectivities S-ij(infinity) = gamma(infinity)(i)/gamma(infinity)(i) and the capacities k(i) = gamma(infinity)(i) at infinite dilution. The experimental data with [R1 R21M](+)[BTI](-) were compared with the predicted results using mod. UNIFAC (Do). The predicted results are in good agreement with the experimental data. (C) 2008 Elsevier B.V. All rights reserved.