Among several proposed enhanced oil recovery (EOR) methods, smart water injection is one of the most widely examined methods due to its unique advantages on wettability alteration. Besides, another well-known EOR method is surfactant flooding, which has a strong capability of altering both the IFT and the rock wettability. Thus, the current study is concentrated on the application of these two methods combined using Design Expert (DE) and Response Surface Methodology (RSM) approaches to make the measurements more systematic. Furthermore, for the purpose of this study, a cationic surfactant, namely, C12TAB and salts such as NaCl, Na2SO4, MgCl2, and CaCl2 are utilized. Contact angle measurements using constant concentrations of ions and C12TAB are performed to find the best operating conditions followed by the core flooding experiment. In summary, the obtained results revealed that the combination of ions and C12TAB is capable of changing the contact angle from 90° to 14 o while surfactant solution without divalent ions alters the wettability from 90° to 71°. Moreover, the results demonstrated that a combination of C12TAB and monovalent ions is less effective than a combination of C12TAB and divalent ions. Finally, the core flooding results illustrated that it is possible to achieve the ultimate oil recovery of about 43.7 to 90.66 based on original oil in place (OOIP). © 2020, © 2020 Taylor & Francis Group, LLC.