Enhanced oil recovery methods are used to recover the percents of oil that are not naturally recoverable from reservoirs. Water injection as a secondary recovery is used to maintain the pressure in water-drive reservoirs. An important point for having a successful injection is the compatibility of injection and formation waters. OLI ScaleChem software predicts mineral scaling potentials of 54 solids for virtually any oil and gas well and processing facility in the world. There are several advantages over other commercially available scaling software: (1) By including all brines in the calculations, the well and processing facility are modeled more accurately; (2) Scaling potential and scale buildup are reported at each calculation point; (3) Automatic correction of pH and charge balance, therefore the chance of unexpected problems from bad water analyses decreases. Also, more effective treatment can be made; (4) Automatical removal of organic acid concentrations from the measured alkalinity, therefore producing a true brine alkalinity; (5) Accurately predict the behavior of any mixture of chemicals in water and mixed solvent. This article presents the predicting of barium sulfate scale tendency of formation water, injection water, and mixing of injection water with formation water at different conditions. The experimentally measured chemical analyses of formation water and injection water were used by OLI ScaleChem software to determine the tendency of scale formation at different conditions. As pressure and temperature were increased, the scaling tendency of the barium sulfate scaling brine was found to decrease, as was predicted by OLI ScaleChem software.