An equation of state (EOS) using an improved expression of the coordination number model for square well (SW) fluids with variable well width was applied for vapor-liquid equilibrium (VLE) calculations of non-polar fluid mixtures and polymer solution. This modified coordination number model was compared with other equations in literature. Better agreement with molecular simulation data for fluid mixtures is observed from this study. Pure fluid parameters for non-polar low molecular weight compounds and polymers are reported. Satisfactory calculated results for the saturated properties are obtained. VLE calculations on non-polar fluid mixtures and polymer solutions were investigated using the van der Waals mixing rules. The equilibrium pressures, solvent solubility and activity of various binary systems were evaluated. This EOS presents comparably good results in comparison with those from other engineering models. (c) 2005 Elsevier B.V All rights reserved.