In many recent studies, optimizing the concentration and type of ions in injection water has led to effective improvements in oil recovery. In this research, the effect of crude oil type and different aqueous solution compositions on the interfacial properties and critical micelle concentration (CMC) of the cationic surfactant CTAB was experimentally investigated. Two crude oil samples with API gravity of 27.3 and 32.3, differing in asphaltene and resin ratios and with slight differences in total acid and base numbers, as well as in hydrocarbon phase compositions (saturates and aromatics), were used. The experiments included measuring dynamic and equilibrium interfacial tension (IFT) in the presence of deionized water (DW), seawater (SW), and engineered Persian Gulf seawater with the doubled concentration of divalent ions (SO₄²⁻, Ca²⁺, Mg²⁺) (ITW). Although the IFT for both crude oils in the presence of salt reached below 0.1 mN/m, the CMC analysis showed that for the lighter oil (32.3 API) in the presence of ITW, the CMC value decreased to 75 ppm, while for the heavier oil (27.3 API), it remained almost constant at 200 ppm. The lighter oil, with more resin and less asphaltene (higher asphaltene/resin ratio and lower colloidal instability index), provided more favorable conditions for CMC reduction and micelle formation. Adsorption kinetics analysis also showed that the adsorption time (τ) for the light oil in the presence of ITW is shorter, indicating faster surface process kinetics in this system. Overall, the results demonstrated that the synergy between the active ions in smart water and the CTAB surfactant can effectively reduce IFT and CMC, and improve conditions for advanced oil recovery. The findings of this study clearly show that the resin-to-asphaltene ratio and the colloidal instability index play a key and decisive role in the surface activity of brine-surfactant systems.