The cost of meeting standards for conventional pollutant emissions is a perennial bone of contention in arguments over vehicle emission regulations. The public health benefits of the most stringent standards have been repeatedly and conclusively demonstrated, and the control technologies are readily available. Nevertheless, countries with the largest vehicle markets worldwide differ greatly in the rates at which they are willing to adopt the most stringent emission standards-and some of those whose populations would benefit most lag furthest behind. Among the reasons often given for delaying the implementation of stricter standards is the extra cost added to the vehicle by the emission control system.This two-part series paper assesses separately the cost of emission control technologies for gasoline and diesel light duty vehicles. In part one, the paper addresses the cost of gasoline light-duty emission control technology by regulatory level, from early stages to upcoming levels. Focus is given to Three-Way Catalytic converters. Technologies and costs are studied for the two main regulatory programs followed globally, the European and the U.S. emission standards. The paper presents an update on early U.S. and EU emission standards compliance costs as the original estimates have never been updated to reflect actual experience and incorporate the substantial improvements in emission control technologies and reductions in cost that have occurred over time. The paper assesses the costs of required technologies in current terms, using both direct and indirect methods to account for technology changes, correct for inflation, and pull in feedback from experts. Estimates reveal that the cost of taking a 2.0 L, 4-cylinder vehicle, from Euro 1 technology controls to the most stringent proposed EU standard (Euro 6) is close to US$150. Similar costs are found for technologies following the US program.