Most of the world’s oil is found in carbonate reservoirs which are formed from minerals such as calcite. Only 30-35% of original oil in place can be extracted using the improved oil recovery methods. To increase the oil extraction, enhanced oil recovery (EOR) method is used. EOR uses chemicals (surfactants, alkaline, polymer etc.) to alter the wettability of oil towards the rock surface. Several studies have shown that injecting water with specific ionic composition and concentration into a carbonate reservoir can alter its wettability toward a more water wet scenario, thereby resulting in higher oil recovery. However, a comprehensive explanation and understanding of the wettability alteration mechanism has not emerged. Here, classical molecular dynamics simulations are used to understand the wettability alteration phenomena in presence of inorganic salts at the molecular level.