The aim of this work is to summarize our systematic studies on activity coefficients at infinite dilution (gamma(infinity)(12)) of various organic compounds and water in 1-n-alkyl-1-methylpiperidinium cation-based ionic liquids with bis[(trifluoromethyl)sulfonyl]imide anion, [C(n)C(1)Pip][NTf2] (n = 3-6). New sets of experimental data measured by gas-liquid chromatography are reported for 43 different solutes in [C(5)C(1)Pip][NTf2] and [C(6)C(1)Pip][NTf2] in temperature range T = (308.15 to 358.15) K. Moreover, ambient pressure liquid densities of those ionic liquids are presented at different temperatures. The results are discussed in terms of an influence of structure of both solute and ionic liquid on gamma(infinity)(12). Capabilities of the studied ionic liquids in liquid-liquid extraction of aromatics or sulphur compounds from aliphatic hydrocarbons are demonstrated in terms of infinite dilution selectivity and capacity. Finally, linear solvation energy relationship (LSER) theory and regular solution theory (RST) were used to analyze the obtained experimental data. In particular, correlative and predictive power of the most current version of the LSER is demonstrated and the Hildebrand's solubility parameters are calculated as a function of temperature by using the RST. (C) 2013 Elsevier Ltd. All rights reserved.