In this work. a new method to determine a suitable repulsive term for cubic equations of state is introduced. Based on this method and by using a simplified molecular theory of hard-core fluids, a new two constant parameter cubic equation of state is presented. The proposed equation of state is applied for PVT and VLE calculations of different pure fluids and fluid mixtures. The results are compared with those obtained by two commonly used cubic equations of state. The comparisons indicate that the new equation of state yields better results.