A variety of exhaust emission regulations exist in the world today, establishing different testing procedures (many with different driving cycles) and emission limits. Vehicle manufacturers competing in the international marketplace must develop technologies to meet the mandated performance levels, and then run different tests to demonstrate compliance. In addition, manufacturers face different national administrative and production conformity requirements. The need for so many different procedures is questioned. Technologies to meet current emission requirements divide the world markets for passenger cars and light commercial vehicles into two divisions, one where catalytic converters and unleaded gasoline are needed and the other where leaded gasoline can be used. Adoption of a single test and compliance procedure for each of these two situations is proposed. The advantages of such harmonization are discussed.