Knowledge of the phase behavior of condensate gas systems is important for predicting reservoir performance and future processing needs. In this communication, new improved models are developed to calculate the gas phase and two phase compressibility factors based on constant volume depletion (CVD) analysis of the well stream effluent at any depleted state in retrograde gas condensate systems. These methods are based on compositional analysis of more than 1300 compositions of gas condensates collected worldwide. The average absolute relative deviation and correlation coefficient of the developed models from experimental gas phase and two phase compressibility factor values were about 0.73% and 0.998 and 1.30% and 0.992, respectively. This study also presents an evaluation of 120 possible methods of calculating the gas compressibility factor for gas condensates. The accuracy of the new models has been compared to all 120 methods. The comparison indicates that the proposed models are consistent, reliable, and superior to all the methods.