This paper is the third one in a series in which a new strategy for modeling heavy petroleum cuts is proposed, with which the PVT properties of gas condensate and crude oils can be completely predicted using a classical one-fluid model with a cubic equation of state. In the second paper in this series, a new method of characterizing petroleum cuts was described. It was concluded that it was necessary to have at least one experimental saturation pressure in order to be able to calculate the PVT properties of a reservoir fluid with a good degree of accuracy. The third paper focuses on the development of a method which can be used to estimate the upper saturation pressure of reservoir fluids at about 100 degrees C, The parameters used in the model were based on correlations involving more than 70 experimental saturation pressures. The method described in this paper, along with the characterization procedure described in the previous paper, makes it possible to completely calculate the PVT properties of a given reservoir fluid. Comparisons are made with other calculation methods described in the literature, and results obtained during gas injection experiments (swelling tests) are discussed.