Previous pseudo-phase representations of micellar/polymer phase behavior have been highly successful in simulating enhanced oil recovery processes using conventional numerical methods. These models allowed for a variety of physical phenomena, such as the formation of one to three phases, the effect of salinity and co-solvents on the phase behavior, adsorption of several of the chemical species, capillary desaturation, and polymer shear thinning and permeability reduction. In order to extend these models to either higher-order simulation techniques or to contaminant transport problems, it is necessary to remove previous discontinuities in the model behavior and to improve the predictions as concentrations become infinitesimal. In this paper, we provide a complete description of a revised model that avoids the problems of the previous model, and we show how to implement the computations in a numerically stable fashion. Computational results from a North Sea pilot study are presented.