The use of water-alternating-gas injection can potentially lead to improved oil recovery from the fields; simultaneous water and gas injection is a form of water-alternating-gas injection. However, there is still an incomplete understanding of these processes and the need for comparative work is inevitable. Core flood experiments and compositional simulations of water-alternating-gas and simultaneous water and gas processes are presented. Immiscible, near miscible, and miscible modes of injection are covered. Matching process is done and optimization of design parameters (injection rate, slug size, water-alternating-gas ratio, and injection gas) is performed. Experimental data demonstrate that simultaneous water and gas injection accelerate oil production as compared to water-alternating-gas injection in all modes of injection, and miscible simultaneous water and gas injection with CO2 produces more than 74% of original oil in place. The simulation results indicate that with different water-alternating-gas ratios (water/gas volumetric) the ultimate oil recovery during simultaneous water and gas injection in operational range (water-alternating-gas ratios between 0 and 2) is almost independent of water-alternating-gas ratio.