Phase behavior of the surfactant AS41-octane system has been measured as a function of salinity and surfactant concentration. Optimal salinity increased when increasing surfactant concentration in brine containing both mono- and divalent ions. Comparing core floods performed with constant salinity and salinity gradients showed that lowering the salinity of the drive-water helped to maintain a better phase behavior. Retention of chemicals was also lowered, due to no phase trapping of surfactants. Modeling of phase behavior is improved using the program FASE. The main improvment in FASE is the unsymmetrical binodal curve. This improvement is important for successful prediction of surfactant displacement. 6 refs., 17 figs., 12 tabs.