In this work we examined the prediction of vapor-liquid equilibria (VLE) of mixtures from the combined use of the Peng-Robinson equation of state (PR EOS) and the COSMO-SAC liquid activity coefficient model (LM). Based on the results of quantum mechanical calculations, it has been shown that the COSMO-SAC model is capable of predicting VLE of mixtures away from the critical point of any constituent component. Following the Wong-Sandler mixing rule, we found that the combined model is capable of predicting the VLE of binary mixtures, including alkane and alkane, alkane and alcohol, alkane and ketone, and alcohol and water, over a wide range of temperature (183.15-623.15 K) and pressure (0.1-19 MPa). Furthermore, it is found that the accuracy can be greatly improved when the Stavermann-Guggenheim combinatorial term in the COSMO-SAC model is ignored. The average error in both the pressure and vapor phase composition from the latter approach, denoted as PR + WS + COSMOSAC(res), is lowered by more than 50% compared to that from the PR EOS with the van der Waals one fluid mixing rule (PR + VDW). Ourresults show that PR + WS + COSMOSAC(res) is a promising approach for mixture VLE predictions over a large range of conditions. (c) 2007 Elsevier B.V. All rights reserved.