Algorithms that are commonly used for the evaluation of water saturation can require different input values of saturation exponent for meaningful application to the same reservoir rock. Further, the differences in the required saturation exponent can vary according to the reservoir properties themselves. By taking account of these different input requirements, it is shown that the discrepancies between predicted water saturations obtained using dissimilar petrophysical algorithms can be confined to a restricted range. The procedure is synthesized for easy operational application of an ordered, interactive method that allows a fit-for-purpose saturation exponent to be identified. Through this process, the sensitivity associated with the choice of an interpretative model for the evaluation of water saturation is demonstrably contained. The application of the method therefore increases confidence in petrophysical interpretation by limiting uncertainty.