This work presents a laboratory phase behavior study of Sodium Stearate/brine/oil system. The quantitative and qualitative observation of the phase behavior of the microemulsion in a three phase brine/oil/emulsion system is reported (Winsor III). The experiments were designed to investigate the stability, interfacial tension (IFT), and viscosity of the emulsion phase in a wide range of temperature (25-60 °C), water-to-oil ratio (0.2 to 5), salinity (10 to 200,000 ppm), and surfactant concentration. The range of parameters was selected as what typically occur during a chemical enhanced oil recovery (EOR) process. The effect of pH variations was also studied by changing that of the system from 1 to 11, using different acid and alkalines. As the pH increases, the stability of the emulsion phase increases as well as the emulsion phase thickness. The viscosity of the emulsion phase was also monitored qualitatively for different temperatures. Moreover, using longer chain alkanes confirms the capability of the surfactant for chemical EOR process.