In the petroleum industry, Enhanced Oil Recovery (EOR) technology has been developed to obtain increased oil recovery from reservoirs. One of the EOR methods is chemical EOR using a surfactant known as the surfactant flooding method. Surfactants have the ability to reduce the interfacial tension between oil and water in the rock matrix so that residual oil can be produced. There are several parameters that affect the performance of surfactants, among which will be discussed in this discussion, namely the middle phase emulsion obtained from the phase behavior test and the results from the Interfacial Tension (IFT) test. Based on the literature review, the method used in IFT uses the spinning drop method. Compatibility test of Fir wood SLS surfactant solution used with a concentration of 0.5% - 3% and a salinity of 4,000 - 110,000 ppm.