Gas-liquid equilibrium in mixtures containing supercritical carbon dioxide and an ionic liquid has been modeled using the Peng-Robinson equation of state and the interesting modification proposed by Kwak and Mansoori. The proposal is based on statistical-mechanical arguments and on the fact that mixing rules are for constants of an equation of state and not for functions such as the alpha expression that makes the attractive term temperature dependent. Experimental data for mixtures containing carbon dioxide and ionic liquids were obtained from literature sources and the adjustable parameters of the mixing rules were found by minimizing the errors between predicted and experimental bubble pressure. Results were compared with experimental data and with results of other classical mixing rules, such as the proposal of Wong and Sandler. The deviations in correlating gas-liquid equilibrium found with the model Peng-Robinson/Kwak-Mansoori are lower in general than the results obtained with other models. (C) 2012 Elsevier B.V. All rights reserved.