The solubility behavior of solid and fluid components with supercritical fluids (SCF) is investigated using a mean field equation of state. When densities, instead of the more commonly used mole fraction and pressure, are used to illustrate solubilities, the effect of the solute’s vapor pressure becomes clear. An expression for the relation between the solubility and the second cross virial coefficient is derived. The effects of size and interaction energy are investigated by changing the solute and solvent parameters.