In this paper we have established the equation of state (EOS) for liquids. The EOS was established for hard-sphere (HS) fluid along with Lennard–Jones (LJ) fluid incorporating perturbation techniques. The calculations are based on suitable axiomatic functional forms for surface tension $S_m (r )$, $r \geq d/2$ with intermolecular separation 𝑟, as a variable, and 𝑚 is an arbitrary real number (pole). The results for $\beta P/ \rho$ from the present EOS thus obtained are compared with Percus-Yevick (PY), scaled particle theory (SPT), and Carnahan–Starling (CS). In addition, we have found a simple EOS for the HS fluid in the region which represents the simulation data accurately.

It is observed that, this EOS for HS gives, PY (pressure) for $m = 0$, CS for $m = 4/5$, whereas for $m = 1$ it corresponds to SPT.

Author uses the condition in terms of contact point radial distribution function $G(\sigma, \lambda(\eta_c, \alpha))$ containing the self-consistent function $\lambda(\eta_c, \alpha)$ and condition of continuity at $\sigma/2$ = contact point, to determine equation of state, (EoS). Different EoSs in terms of built-in parameter, 𝑚, can be obtained with a suitable choice of $\lambda(\eta_c, \alpha)$ and the present EoSs have less r.m.s. deviation than Barker–Henderson BH2 for LJ fluids, and results are much closer to molecular dynamics (MD) simulations than expectations and reproduce the existing simulation data and present EoS for LJ potential, with the help of a set of minimum single-scaled parameter, $a_0(\eta_c, \alpha)$ for a given reduced temperature, $T^\ast = (1/\beta \epsilon)$= 1.4, 2, 3, 4, 5, 6. It has been found that parameter 𝛼 = 1.059128388 can be used to fix up the critical temperature parameter $T_c$ = 1.3120(7) to that of a computer simulation result.