In this work, Wagner's formulation and methodology for the representation of vapor pressure data have been extended by using new basis functions, obtained by analytical integration of Clausius-Clapeyron equation assuming a Watson like formulation for the heat of vaporization. The proposed rational base functions are more flexible and lead to higher accuracy in data fitting, comparing favorably to Wagner's equations. Even for a few components, a general pattern has not been identified, and, as clearly mentioned by Wagner, it is mandatory to use stepwise regression in order to retain the most relevant terms for a given number of parameters; this is required by the increased flexibility of the proposed function basis. (C) 2013 Elsevier B.V. All rights reserved.