The Henry's Law constants of CO2, CH4 and N-2 in 2701 ionic liquids (ILs) of widely varying structures at (283.15, 298.15, and 323.15)K, the molar volumes and the relative polarity of ILs at 298.15 K are predicted using the thermodynamic method COSMO-RS. Structural variations in the cations and anions that enhance or diminish solubility and selectivity are identified. The trends in Henry's Law constants are explained in the light of molecular interactions qualitatively through sigma profiles and sigma-potentials of ILs. The relationships between the Henry's Law constants and the properties of ionic liquids are also investigated. In general, the Henry's Law constants of CO2 decrease with increase in molar volume, and decrease in polarity of ILs. Both the solubility of CO2 and selectivity decrease as temperature is increased. Activity coefficients at infinite dilution, enthalpies and entropies of solvation are also used to elucidate gas-liquid interactions. COSMOtherm predictions are compared with experimental data. Ranking of cations, in terms of Henry's Law constants, is reported for each counterpart anion and vice versa. Such information is useful for designing and screening of ionic liquids for CO2 capture. (C) 2011 Elsevier B.V. All rights reserved.