Effective hard sphere diameters for non-spherical molecules were obtained through use of the corresponding states principle and hard sphere expansion theory. The Weeks Chandler Andersen "blip" function technique, with an expanded form of the Verlet and Weis equation, was utilized to fit potential parameters for several models. In this manner, an equation was developed to predict effective hard sphere diameters. Intermolecular potential functions were developed with a three parameter Mie model and second virial coefficients. The numerical values of the Mie intermolecular potential model were compared to the more commonly used Lennard-Jones intermolecular potential model. Effective hard sphere diameters were evaluated from P-V-T data. Dimensionless plots of the effective hard sphere diameters were prepared.