C Chemical injection acts to drain the remaining oil in the reservoir which iscalled the residual oil saturation or SOR. It occurs as a result of waterfloodexperience fingering or events which water through oil , by that polymer isrequired as a suppressor fluid additive to increase the viscosity which improvesthe mobility control of the fluid suppressor that can increase sweep efficiency and minimize SOR. In this case the salinity of formation water can damage thechemical bonds of the polymer thus degrade the performance of the polymer. In the experiments of this thesis five salinity of formation water is used which are 1000 ppm, 5000 ppm, 10,000 ppm, 35,000 ppm, and 50000 ppm. In thisexperiment the polymer that is used is a starch polymer. It is a bio-polymer made or based on potatoes. Polymer concentration used in this experiments are 1000 ppm and 5000 ppm, respectively analyzed at every fifth salinity of formation water that is used, in order to analyze the correctness of the theory that then formation water salinity can damage the chemical bonds of polymer and lower its performance to decrease SOR and Increase RF. After experimenting with both polymer concentrations and five salinity it’s showed that the salinity of the formation water completely degrade the performance of the polymer which can be seen from the decline in the value of RF =and SOR along with the increase of the value of the formation water salinity. Thus, it can be concluded that the salinity of formation water injection degrade the performance of the polymer in the polymer injection to increase the RF and lower the value of SOR.