ABSTRACT: In order to reduce the anthropogenic greenhouse-gas emissions, CO 2 geological storage has been proposed. Many applications for CO 2 geological storage exist, such as injecting CO 2 into depleted hydrocarbon reservoirs, enhanced coalbed methane recovery, and enhanced oil recovery (EOR) operations. CO 2 injection has been extensively studied by many researchers and has resulted in large oil recoveries. Injecting CO 2 alone experienced an early breakthrough problem, which is unfavorable in CO 2 sequestration projects. CO 2 must be kept inside the oil reservoir. This pushes researchers to combine water with CO 2 flooding to improve the sweep efficiency. In this study, we investigated the effect of water salinity on CO 2 flooding and on the water–rock interactions during WAG. The results of this study show that combining LS water with CO 2 flooding prevents early breakthrough by improving CO 2 sweep efficiency. The oil recovery was also high due to merging LS water with CO 2 flooding. Controlling the injected water chemistry has a large influence on both oil recovery and CO 2 solubility in crude oil. The highest effect of added chemicals can be ranked in an order of NaCl> CaCl 2 > Mixed NaCl, CaCl 2 , and MgCl 2 >MgCl 2 .