Many experimental studies have been undertaken to measure interfacial tensions (IFT's) as a function of pH, salinity, temperature, and divalent ion concentrations. This behavior varies from one crude oil to another and is critical in determining its suitability as a candidate for caustic flooding. A model based on a thermodynamic analysis of crude oil/caustic interfaces has been developed that predicts the IFT behavior of such systems. The model accounts for IFT variations with changes in pH, salinity, and temperature by using parameters that must be estimated from a preliminary experimental study. The model predictions compare well with earlier reported experimental results. It is shown that the application of such a model to empirical correlations for residual oil saturations and fractional flow and relative permeability curves for an alkaline flood with selfsharpening fronts if the injection pH and salinity are specified. The basic equations needed to extend this model to account for divalent ions and more complex flow systems are provided in the Appendices.