In this work, we apply an equation of state based on statistical-mechanical perturbation theory to liquid natural gas mixtures. Three temperature-dependent parameters are needed to use the equation of state: the second virial coefficient, B-2(T), an effective van der Waals covolume, b(T), and a scaling factor, alpha(T). The second virial coefficients are calculated from a correlation based on the surface tension, gamma(tr) and the liquid density at the triple-point, p(tr). alpha(T), and b(T) can also be calculated from second virial coefficients by a scaling rule. Based on the theory, these two temperature-dependent parameters depend only on the repulsive branch of the potential function, and therefore, by our procedure, can be found from gamma(tr) and rho(tr). The theory has a considerable predictive power, since it permits the construction of the p-V-T surface from the surface tension plus the triple-point density. The equation of state is tested on 27 Liquid mixtures. The results indicate that the liquid density can be predicted within about 5%, over a range of temperature.