This paper examines the steady state hydrodynamics of a fluidized bed of two particle species, having different diameters and densities. Steady state mixing solutions of the volume-averaged equations of motion for the fluid and particles are sought. An expression for the fluid particle interactive force (in the mixture) is postulated to close the continuum equations of motion using an excluded volume assumption. Solutions to the equations are found for a fluidized bed of glass beads and carbon char in water. It is shown that the solution sets not only characterize the composition and expansion behavior of the mixing states, but also provide a description of the observed phenomenon of "layer inversion". The model identifies three possible layer inversion scenarios, one of which has been observed experimentally. Comparison with experimental data suggest that the hydrodynamic mechanism Of fluid-particle interaction is not fully captured with an excluded volume assumption. Thus, we show how experimental data can be used to derive functional forms for expressing the complex hydrodynamic behavior within the framework of the model.