A thermodynamic model based on the perturbation theory is investigated. The perturbed hard-sphere chain (PHSC) equation of state (EOS) is applied to calculate phase behavior of the binary systems containing supercritical carbon dioxide. A calculation program is written. The vapor-liquid phase equilibrium calculation is conducted with the binary systems and a comparison is made between the calculation results and experimental ones. It is shown that the PHSC equation of state can be reliably used for calculating the vapor-liquid phase behavior of carbon dioxide systems when the pressure is very high. (C) 2003 Elsevier B.V. All rights reserved.