A simple mixture model based on the mixture pair correlation functions was developed and tested. For a Lennard-Jones fluid, the new model showed high accuracy when compared to simulation data. The model was compared to the van der Waals model, the dense fluid theory model and the more complex perturbation model of Weeks-Chandler-Anderson, Lee-Levesque and Grundke-Henderson (WCA-LL-GH); it showed a comparable accuracy to the latter. For hard sphere molecules, the model predictions are comparable to the accurate Mansoori-Carnahan-Starling-Leland equation for mixtures of hard spheres. However, at high densities, an abnormal behavior was observed for small concentrations of the larger component, when the model is used with the Carnahan-Starling equation of state for the pure hard spheres. This might point to phase separation or to a limitation of the new model under the conditions studied. A procedure for extending the model to non-spherical and polar molecules is suggested.