Solubility data of carbon dioxide (CO2) in the ionic liquids 1-alkyl-3-methytimidazolium bis(trifluoromethylsulfonyl)imide ([C-n-mm][Tf2N], n = 2, 4, 6, 8) are presented at pressures up to about 45 MPa and at temperatures between 25 and 70 degrees C. The equilibrium pressure increased very steeply at high CO2 compositions. The increase in the alkyl chain length on the cation of the ionic liquids increased the CO2 solubility. The experimental data for the CO2 + ionic liquid systems were correlated using the Peng-Robinson equation of state. (C) 2008 Elsevier B.V. All rights reserved.