To promote CO2 utilization and protect the environment, CO2 is often employed to enhance oil recovery. Meanwhile, injection of CO2-CH4 mixtures can offer better mobility ratios and delay water breakthrough resulting in the favorable oil sweep efficiency. The gas-alternating-water (WAG) flooding in rhythmic hydrocarbon reservoirs has been studied by simulation software. The difference between water and CO2-CH4 flooding lies in the different density and viscosity among CO2, CH4, oil and water. Water tends to displace oil along the lower reservoir; inverted rhythmic reservoir may slow down the trend. CO2 and CH4 tend to displace oil along the middle-upper and upper reservoir, respectively; positive rhythmic reservoir may slow down the trend. Therefore, a homogeneous reservoir should be given priority in WAG flooding, followed by positive rhythmic reservoir. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.