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Diesel vehicles have significant advantages over their gasoline counterparts including a more efficient engine, higher fuel economy, and lower emissions of HC, CO, and CO2. However, NOx control is more difficult on a diesel because of the high O2 concentration in the exhaust, making conventional three-way catalysts ineffective. The most promising technology for continuous NOx reduction onboard diesel vehicles is Selective Catalytic Reduction (SCR) using aqueous urea. Recent work with urea SCR has involved aftertreatment for the 1.2L DIATA common-rail diesel engine. This engine was used in Ford's hybrid-electric vehicle, the Prodigy, which was developed under the PNGV (Partnership for a New Generation of Vehicles) program. An emission control system consisting of a diesel particulate filter followed by an underbody SCR system was used successfully to meet ULEV emission standards (0.2 g/mi NOx, 0.04 g/mi particulate matter (PM)).