The (rho, T,rho) and (vapor + liquid) equilibria for fluid mixtures containing either CO2 or H2S have been determined from 13 equations of state. The estimated values have been compared with published experimental results. CO2 and H2S were used to represent non-polar and polar fluids, respectively. The equations of state investigated were as follows: (a) the Lee-Kesler equation; (b) two equations that included new reference fluids for the Lee-Kesler method; (c) three so-called extended equations of state; and (d) seven cubic equations of state. After adjustment of the binary interaction parameters the predicted values differed from the experimental data by about 0.8% for CO2 mixtures while for H2S mixtures the uncertainty was about +/-2.8%. Somewhat larger errors, although still lower than +/-5%, were obtained for co-existing phase densities; the Lee-Kesler method provided results of the highest accuracy. The cubic equations proposed by Schmidt and Wenzel and Valderrama provide the most reliable predictions of both single and co-existing phase densities. Comparison of the predicted (vapor + liquid) equilibrium with experiment shows that each of the seven cubic equations provides results of similar accuracy and all within +/-6%. (C) 2003 Elsevier Ltd. All rights reserved.