Abstract In most water injection projects, inhibitors are added to the injected water to protect the pipelines, facilities, and reservoir from corrosion, scaling, and bacteria growth. Most studies in the literature focus on the efficiency of inhibitors to prevent corrosion and scale, but very few discuss their effect on formation permeability and oil recovery. Laboratory experiments on core samples were carried out and chemical additives to seawater were tested at different conditions to evaluate formation damage and residual oil saturation. Different solutions of combined scale, corrosion, and biocide inhibitors at concentrations of 0.5 and 1% were added to seawater. Formation damage was studied using core samples at full water saturation and showed permeability decline up to 75% due to suspended solids formed from the interaction between the inhibitors and dissolved salts in water. Oil recovery was measured using core samples at full oil saturation. Residual oil saturations varied between 24 to 70% depending on the type and concentration of inhibitors. An increase in the concentration of a single inhibitor yielded a reduction in oil recovery. However, for mixture of inhibitors, the relationship becomes complex. A linear model developed to predict residual oil saturation from inhibitor concentration and an optimum concentration of the mixtures minimizing permeability reduction and residual oil saturation was defined.