To determine the ISM equation of state, we have established a new reduced temperature scale T-ES* = T-ES* (T; E-S, rho (f)), where Tis the absolute temperature, E-S and rho (f) are surface energy and the liquid density at the freezing temperature, respectively. The reduced second virial coefficient B-2* follows a promising corresponding states correlation for a number of spherical, linear and long chain hydrocarbons liquids, allowing prediction of B-2(T) in the desire temperature range. Then it follows that all three temperature-dependent parameters of the ISM equation of state can be determined from only two scaling constants E-S and rho (f). The method we present has advantages over previous methods in that E-S is state independent, and it can be used to simplify the application to mixtures. That is, only two (rather than three) scaling constants E-S and rho (f) of the mixture components are combined. On the other hand, E-S involves the surface entropy and thus, T-ES*, turns out to represent a real thermodynamic quantity that is of concern in theoretical investigations. The applications to the compressed and vapor-saturated liquids of wide range of acentric factors and their mixtures result in densities within less than 5% of the experimental values.