In 2004, we started to develop a group contribution method aimed at estimating the temperature dependent binary interaction parameters (k(ij)(T)) for the widely used Peng-Robinson equation of state (EOS). Because our model relies on the Peng-Robinson EOS as published by Peng and Robinson in 1978 and because the addition of a group contribution method to estimate the kij makes it predictive, this model was called PPR78 (predictive 1978, Peng Robinson EOS). In our previous papers eleven groups were defined: CH3, CH2, CH, C, CH4 (methane), C2H6 (ethane), CHaro, C-aro, C-fused (aromatic rings), CH2,cyclic and CHcyclic = C-cyclic. It was thus possible to estimate the k(ij) for any mixture containing alkanes, aromatics and naphthenes at any temperature. In this study, the PPR78 model is extended to systems containing carbon dioxide. To do so, the group CO2 was added. The results obtained in this study are in many cases accurate. (C) 2007 Elsevier B.V. All rights reserved.