Abstarct: bstract Water Alternating Gas (WAG) injection is one of the common methods for oil displacement in porous media. This method of injection has many engineering and environmental applications, including soil remediation or enhanced oil recovery from underground reservoirs. The alternating presence of water and gas combines gas compressibility with the high mobility of water to increase the displacement efficiency and recovery. The transport properties of porous media and heterogeneity, among other parameters, play a significant role in the efficiency of immiscible WAG injection. To extend the fundamental understanding required to describe how porous media characteristics influence WAG injection efficiency, we conducted a comprehensive series of experiments under well-controlled laboratory conditions. Three types of porous media were manufactured with a 3D printer in our investigations. The first medium has single permeability, the second one is fractured, and the third one is a medium with dual permeability. The porous media were saturated with silicone oil. Nitrogen and water were used to displace oil under different WAG ratios of 4:1, 2:1, 1:1, 1:2, and 1:4. High-resolution imaging was used to quantify the dynamics of displaced oil and patterns. The recorded data enabled us to investigate the combined effects of injection conditions and the presence of fracture as well as permeability contrast on the displacement efficiency. The oil recovery was the highest under WAG ratio of 1:1, i.e., the equal slug size of the water and gas. The results showed that the WAG ratio of 1:1 injection in the S medium recovered 55% of the oil, while the presence of the fracture and permeability contrast in the F and D medium led to the displacement recovery efficiency of 36% and 47%, respectively. Additional insights were obtained through the recorded pressure drop evaluation, and the superiority of the WAG ratio of 1:1 injection was explained through the pressure drop diagram. Our experimental data and analysis offer new insights regarding the effects of heterogeneity on the efficiency of WAG injection in porous media under different boundary conditions.