<div class="htmlview paragraph">In 1972 models for sale in California, Buick first employed programmed-metered exhaust gas dilution of the engine intake charge as the major means of reducing Oxides of Nitrogen (NOx) emission levels.</div> <div class="htmlview paragraph">With more stringent NOx emission standards applicable nationally to 1973 light duty vehicles, it is probable that similar systems will be more widely used.</div> <div class="htmlview paragraph">The major considerations in the decision to use this means of reducing NOx emissions, the design details of the total system, and the field experience to date is discussed.</div> <div class="htmlview paragraph">The author concludes with some thought on the limit of usefulness of Exhaust Gas Recirculation for NOx reduction, and further refinements needed to approach that limit.</div>