The steam-assisted gravity drainage (SAGD) process which is known as economical and effective oil recovery method in oil sands plant requires several separation equipments due to the nature of process. Among them, the free water knock out (FWKO) vessel is used as the primary and largest multi-phase separator and consists of various internal separation devices. Porous baffle is one of the important internal devices that can improve separation efficiency by mitigating sloshing and stabilizing liquid phase. In this study, the effect of the porosity and arrangement of porous baffle on the separation performance was numerically investigated using pseudo-transient analysis. The velocity vector field and volume fraction were calculated and graphically depicted to analyze the stabilization of liquid phase. In addition, oil mass flow rate and water cut were employed to evaluate the separation efficiency of FWKO vessel.