Wettability alteration has been proposed as one of the dominating effects of engineered salinity waterflooding (EWF). Most of the existing approaches for modeling wettability alteration and enhanced oil recovery by EWF often oversimplify, if not ignore, the critical role of geochemical reactions at both rock− brine and oil−brine interfaces in this process. Therefore, this paper presents a new approach wherein the flow simulation and salt transport are explicitly coupled with geochemical calculations based on bond product sum (BPS). In the BPS method, the surface complexation reactions at oil−brine and rock−brine interfaces are integrated and then used as basis for wettability alteration modeling during the flow simulation. The wettability alteration is accomplished by incorporating an interpolating parameter (θ) to update locally relative permeability and capillary pressure as a function of brine composition. This approach directly accounts for the effect of water composition and pH, oil composition (acid number and base number), and surface reaction site densities on EWF performance. Moreover, it can distinguish between directly and indirectly adsorbed oil components, affecting the initial wettability of the system. The method was validated through comparisons of the simulation results with those from published coreflood studies. We report that the directly adsorbed oil components, which promote oil-wetting conditions, aid oil recovery through EWF only under specific pH conditions, especially at pH > 8 for crude oils with high acid numbers. However, this cannot be easily practical for all systems. Conversely, indirectly adsorbed oil components enable mixed-wetting conditions and can enhance oil recovery through EWF. This can be accomplished via employing specific strategies, such as reducing water salinity or modifying the concentration of potential-determining ions (PDIs). The developed BPS-based model improves the prediction of transient oil recovery, particularly before reaching the residual oil saturation (S or ), as it is critically important for field planning and design.