The chemical simulation models, UTCHEM (from the University of Texas at Austin) has been used within the SPOR-Water improved oil recovery research program, in connection with experimental surfactant phase behavior measurements and surfactant floodings. This report summarizes changes and extensions to the phase package part of UTCHEM. The most important changes are: Extension of the binodal curve model to handle asymmetrical binodal curves. This has improved the reliability in phase behavior prediction over a wide range of system conditions; The cation exchange model for interaction between cations and surfactant and mineral surface, is extended to handle an arbitrary number of different cations; A new microemulsion viscosity model calculates phase viscosities as functions of both phase composition and phase type. 16 refs., 30 figs.