A comparative study was made to establish how is altered the performance of Patel-Teja EoS and Peng-Robinson EoS, to represent thermodynamic properties of saturated pure fluids when the alpha function of Soave is substituted by an exponential function with one, two or three parameters. Results show that the Soave function should be replaced by a two parameter exponential function to get adequate representation of the vapor pressure and the saturated vapor volume of pure substances; especially in the low pressure zone (1-101.325. kPa). Additionally the performance of equations of state to represent saturated liquid volume and vaporization enthalpy was found practically independent of the alpha function. Comparison between the two equations of state, show that Patel-Teja EoS is superior than Peng-Robinson EoS to represent the saturated liquid volume of pure substances with critical compressibility factor lower than 0.25 or higher than 0.285. Also it has been demonstrated that using the two-parameter alpha function of Heyen with the Wong-Sandler-NRTL mixing rules the capability of cubic EoS to represent the vapor liquid equilibria below 1. atm for alcohol/alkane and alcohol/aromatic systems can be improved.