A new approach of calculating the parameters of a quartic equation of state (EOS) (Yun et al., Fluid Phase Equilibria 187-188, 275-298 (2001)) was suggested. The parameters of the EOS were correlated to critical constants as well as dipole moment. And the modified quartic EOS was extended to both polar and non-polar substances without any substance-dependent empirical constants which are necessary in the original quartic EOS in calculations of polar substances. To validate the new approach, a list of substances, including polar and non-polar ones, were calculated. The calculated results of both thermodynamic and volumetric properties were obtained with good accuracy.