Vapor-liquid equilibria (VLE) for six systems at 353 K and activity coefficients at infinite dilution (gamma(infinity)) for various solutes (alkanes, alkenes, cycloalkanes, cycloalkenes, aromatics, alcohols, ketones, esters, ethers, and water) in the ionic liquids; 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide [EMIM][BTI], 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide [HMIM][BTI], 1-octyl-3-methyl-imidazolium bis(trifluoromethylsulfoiiyl)imide [OMIM][BTI], and l-butyl-I-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide [BMPYR][BTI] have been determined in the temperature range from (303 to 333) K. Additionally, gamma(i)(infinity) were measured for seven solutes in the binary mixture of [EMIM][BTI] and [BMIMI[BTI]. Furthermore the densities of the investigated ionic liquids were measured in the temperature range from (293.15 to 353.15) K. The new and the already available data for the various systems of imidazolium bis(trifluoromethylsulfonyl)imides [RR'IM][BTI] with alkanes, alkenes, cyclic hydrocarbons and alcohols were used to fit the required group interaction parameters for the group contribution methods original and mod. UNIFAC(Do). The predicted results were compared with the experimental data and the results using COSMO-RS(OI). (c) 2005 Elsevier Ltd. All rights reserved.