Abstract Chu, J.-Z., Zuo, Y.-X. and Guo, T.-M., 1993. Application of the modified Kumar-Starling equation of state to predict the phase behavior of mixtures in the near-critical region. Fluid Phase Equilibria, 81: 17-38. The modified Kumar-Starling (MKS) equation of state (EOS) developed by the authors (Chu, J.-Z., Zuo, Y.-X. and Guo, T.-M., 1992. Fluid Phase Equilibria 77: 181-216) was applied to predict the phase behavior of mixtures containing defined/undefined components. Special attention was paid to examining the performance in the near-critical region. For mixtures containing denned components only, the comparison of the calculated results with well-known equations of state, such as SRK (Soave G., 1972. Chem. Eng. Sci., 27: 1199-1203), PT (Patel, N.C. and Teja, A.S., 1982. Chem. Eng. Sci., 37: 467-477) and the volume-translated SRK (Chou, G.F. and Prausnitz, J.M., 1989. AICHE J., 35: 1487-1496) shows the superiority of the MKS EOS. When applied to undefined component-containing reservoir fluid mixtures, a characterization procedure for the heptane-plus fraction was proposed by the authors. As compared with the calculation results based on SRK-P EOS (Peneloux, A., Ranzy, E. and Freze, R., 1982. Fluid Phase Equilibria, 8: 7-23) and the characterization procedure proposed by Pedersen et al. (Pedersen K.S., Thomassen P. and Fredenslund Aa., 1988. Paper presented at the AICHE Spring National Meeting New Orleans LA, 6–10 March) significant improvements in the prediction of the phase behavior of near-critical oil/gas, and highly aromatic/nitrogen-enriched gas condensates were observed.