A modified form of the Peng-Robinson equation of state is proposed. This equation shows its greatest advantage in the predictions of the volumetric properties in the single-phase region for mixtures, while it performs as good as original Peng-Robinson equation for the predictions of thermodynamic properties of pure components, and vapor-liquid equilibria of mixtures. Also the equation gives apparently more realistic Joule-Thomson inversion curves than both the SRK and PR equations.