A new approach to the analysis of vapor adsorption on solids is proposed. In this method the adsorption isotherm is represented as a(p) = f(p)/(1-p/p(s))(d) where a(p) is the amount of vapor adsorbed, p is the pressure, p(s) is the saturation vapor pressure, f(p) is a function describing the adsorption in the first molecular layer, and d is an adjustable parameter. This model allows one to determine the specific surface area of disperse and porous materials in a way that is not limited by the functional form of the monolayer adsorption isotherm, f(p). In addition, this equation gives a new way to correlate adsorption data over the whole range of p/p(s). Comparison is made with experimental data for the systems Ar-KCl, N-2-KCl, O-2-KCl, N-2-SiO2, and N-2-Al2O3.