Immiscible WAG injection, like a couple of other EOR processes include three phase flow inside the reservoir. In order to conduct an accurate simulation study, a comprehensive understanding of three phase flow models available in commercial simulators is unavoidable. Furthermore, according to experimental works have been done on three phase relative permeability, all the studies from pore scale to field scale works dictate the strong dependency of three phase relative permeability to saturation history. This dependency is more obvious in I-WAG which is characterized by a sequence of three phase drainage and imbibitions cycles. In this study, we will investigate the degree of accuracy of different three phase relative permeability models by comparing them with experimental data. Then, we will show the simulation results of WAG injection using different three phase relative permeability models. Also, two and three phase hysteretic relative permeability models will be investigated and the results of the simulation will be compared to experimental data, showing the accuracy of different models. © 2011 IEEE.