Gasoline Sulfur

Sulfur is a natural component in crude oil that is present in gasoline and diesel unless removed. Sulfur in gasoline impairs the effectiveness of emission control systems and contributes to air pollution. Reducing the sulfur content in gasoline enables advanced emission controls and reduces air pollution.

The Tier 2 Gasoline Sulfur program, finalized in 2000, reduced the sulfur content of gasoline by up to 90 percent, enabling the use of new emission control technologies in cars and trucks that reduce harmful air pollution. The Tier 2 program marked the first time EPA treated vehicles and fuels as a system. The program grew out of a Clean Air Act requirement that EPA consider the need, feasibility, and cost-effectiveness of stronger tailpipe emission standards beginning in 2004. Requirements for use of low-sulfur gasoline enabled use of advanced emission control systems in cars, pickups, SUVs, and vans beginning in model year 2004. Vehicles meeting Tier 2 emission standards are 77 to 95 percent cleaner than earlier models. 

Like the Tier 2 program, the Tier 3 program considers the vehicle and its fuel as an integrated system to reduce the impacts of motor vehicles on air quality and public health. The program sets new vehicle emissions standards and lowers the sulfur content of gasoline to a maximum of 10ppm beginning in 2017. The vehicle standards will reduce both tailpipe and evaporative emissions from passenger cars, light-duty trucks, medium-duty passenger vehicles, and some heavy-duty vehicles. The gasoline sulfur standard will enable more stringent vehicle emissions standards and will make emissions control systems more effective. It will also reduce the emissions of the existing fleet of vehicles.

Learn more about Tier 3 gasoline sulfur program. 

Learn more about Tier 2 gasoline sulfur program.