The role of NiO in three way catalyst systems is explored with respect to transient oxygen storage and water gas shift activity observed in lean-rich-lean exhaust composition changes. Oxygen storage behavior is observed to playa role in fresh catalyst systems but disappears on aging. However, storage phenomena are still observed in the presence of water and can be explained in terms of water gas shift activity. Nickel containing catalysts in which the nickel is highly dispersed readily form a surface nickel aluminate complex which minimizes oxygen storage and water gas shift capability. A proprietary catalyst which contains stable nickel oxide is capable of maintaining higher activity under transient operation after hydrothermal aging.