Vapor pressures computed from nine cubic equations of state (EOS＇s) of the van der Waals form are correlated in corresponding states form using the linear Fitter principle and a simple temperature function anchored at the critical point. The results strongly suggest that cubic equations of state do not conform to the usually assumed linear dependence of fluid properties on acentric factor. The failure of three-parameter cubic equations of state to predict the exact vapor pressure consistent with a specified acentric factor is analysed, and new correlations are presented for the characteristic parameter in Soave＇s cohesion function that minimize this intrinsic error over a wider range of acentric factors. Soave＇s direct procedure for calculation of vapor pressures from EOS is found to be more accurate than all other approximate methods by at least 1 order of magnitude. However, the leading coefficient in Soave＇s equations is shown to be inconsistent with the limiting slope of the vapor pressure curve predicted by the equations of state. New direct expressions are developed that eliminate this inconsistency and give good representation of vapor pressures with fewer adjustable coefficients.