All vehicles sold today are required to meet emissions standards based on specific driving cycles. A dual stage catalyst system, with exhaust temperature control, can provide a robust solution to meet challenging modes of operation such as rapid acceleration and other heavy duty transients. The Ultera technology, developed and successfully implemented on stationary natural gas CHP engines, introduces a second stage oxidation catalyst downstream of a three-way catalyst. Air is injected between the two catalyst stages to provide oxygen required for the second stage reaction that removes additional CO and NMOG. Critical to the process is to avoid the reformation of NOx, a common consequence with similar air injection concepts that have been tried in the past. This is achieved by cooling the exhaust gas prior to the second stage to a temperature range in which CO and NMOG oxidation is extremely effective while no new NOx is created. The objective of this research was to apply this technology to vehicle engines, with the primary differences being gasoline-fuel, direct fuel injection, and more dramatic transient loading. Testing of a ULEV compliant light duty vehicle (LDV), a SULEV compliant LDV, and a European vehicle was conducted using a chassis dynamometer. Various tests outside of the standard drive cycles were applied to simulate other driving conditions. Optimization of control temperature and air- injection flow was studied. Also examined were customized catalyst formulations for enhanced hydrocarbon reduction and low sulfur poisoning. Results showed significant reductions of CO and NMOG, with no negative impact on NOx or fuel economy. Future development work can provide opportunities to further reduce NOx emissions through chemistry and integration with engine operation.