A generalized concept which allows a uniform use of cubic equations of state is introduced both fur pure substances and mixtures. Using a generalized g(E)-mixing rule and a simple three-parameter equation of state, calculations of different kinds of fluid phase equilibria were carried out. Comparing these results to those obtained from two-parameter equations of state and excess models like the NRTL equation, it was found that a higher flexibility is yielded, especially concerning the calculation of the three-phase pressure which is the main aim of this work.