The first widespread introduction of catalytic converters was in the United States automobile market. To comply with the U.S. Environmental Protection Agency's new regulation of exhaust emissions, most gasoline-powered vehicles starting with the 1975 model year are equipped with catalytic converters. These "two-way" converters combined oxygen with carbon monoxide (CO) and unburned hydrocarbons (CnHn) to produce carbon dioxide (CO2) and water (H2O). These stringent emission control regulations forced the removal of the antiknock agent tetraethyl lead from automotive gasoline, to reduce lead in the air. Lead is a catalyst poison and would effectively destroy a catalytic converter by coating the catalyst's surface. Requiring the removal of lead allowed the use of catalytic converters to meet the other emission standards in the regulations.