The rational design of separations in multicomponent systems depends on the quality of vapor-liquid equilibrium (VLE) data and the precision to which these data can be represented. In recent years, new experimental techniques have begun to yield better quality VLE data. Often these data warrant the use of more than two parameters per binary pair, which is common in the empirical Gibbs energy of mixing expressions used to represent such data. In this work, we propose two new expressions for representing the Gibbs free energy of mixing : the four parameter Scott-Wilson and the five parameter Scott-Regular Solution-Wilson. A method for evaluating such expressions is presented, including our proposed technique of predicting gamma(infinity) in a mixed solvent from binary data only. For this, we measured gamma(infinity) in a mixed solvent system using differential ebulliometry.