Based on the van der Waals fluid model, a simple equation of state, unique for non-uniform fluids, is developed. It is applied to the liquid-vapor interface, to derive the density profile in the interfacial region. The density profile is used in conjunction with the gradient theory, to yield an expression for the surface tension of a saturated fluid as a function of temperature and fluid properties. The non-dimensionalized influence parameter of the gradient theory is assigned best-fit values, which are of a unity order of magnitude, as expected. The predicted surface tension values are in good agreement with experimental data, for a variety of fluids. (C) 2004 Elsevier Ltd. All rights reserved.