Cubic equations of state are widely used in refinery and petroleum reservoir industries for the prediction of fluid-phase behavior. Two of the most well-known cubic equations of state broadly accepted in industry are the SRK and PR equations. However, neither the SRK nor the PR equation of state yields the best results for the prediction of liquid densities of polar components and heavy hydrocarbons. An approach is proposed to locate an optimum two-parameter cubic equation of state. A methodology is also proposed to modify Twu's CEOS/A(E) zero-pressure mixing rules to extend the range of application of these mixing rules. The mixing rule developed in this work is incorporated into our new cubic equation of state for the prediction of phase equilibria of highly nonideal chemical mixtures.