Natural gas powered engines are widely used due to their low fuel cost. In order to comply with emissions regulations, an aftertreatment system is utilized to treat exhaust from natural gas engines. Stoichiometric burn natural gas engines use three-way catalyst (TWC) technology to simultaneously remove NOx, CO and hydrocarbon. Removal of methane, one of the major hydrocarbon emissions from natural gas engines, is difficult due to its high stability, posing a challenge for existing TWC technologies. In this work, degreened (DG) and SBC (standard bench cycle) aged TWC catalysts were evaluated and compared under a variety of lean/rich gas cycling conditions, simulating stoichiometric natural gas engine emissions. Methane stream reforming and methane oxidation reactions were performed in the presence of NOx to elucidate the effects of lean/rich gas cycling and oxygen storage capacity (OSC) on NOx and methane reduction during the transient operation on both DG and SBC aged TWC catalysts. These results are expected to provide general guidance for optimization of stoichiometric burn natural gas engines.