The solubility Of CO2 in imidazolium ionic liquids (ILs), 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim][BF4]), 1-hexyl-3-methyl imidazolium tetrafluoroborate ([hmim] [BF4]) and 1-octyl-3-methyl imidazolium teirtafluoroborate ([omim] [BF4]) was determined at 305-25 K and pressures from 1 to 9 MPa. The influence of chain length of alkyl substituents on the imidazolium cation on the solubility of CO2 was investigated. The differences in solubility with chain length are in the sequence [omim][BF4] > [hmim][BF4] > [bmim][BF4]. The solubility data were correlated by the extended Henry's law, and enthalpy, Gibbs free energy and entropy changes were obtained. (C) 2005 Elsevier B.V. All rights reserved.