With the aid of fundamental correlations of statistical mechanics and some assumptions

a simple method for calculating pseudocritical constants of mixtures containing nonpolar and slightly polar components is proposed in this paper. A detailed comparison of pseudocritical constants by this method with that by Lee-Keslers rule has been made. Finally

using this method together with Lee-Kesler tables

compressibility factors for some gas mixtures have been calculated

obtaining good agreement with experimental data.