Top Tier is a program that sets standards for detergent levels in gasoline. The standards are designed to exceed the minimum detergent requirements for gasoline set by the Environmental Protection Agency.
The Top Tier Detergent Gasoline program markets cleaner gasoline alternatives that meet or exceed the EPA's Tier 2 emission standards. Additives in gasoline not meeting these standards can cause engine, intake valve and fuel injector deposits which reduce vehicle responsiveness and engine performance. To use the Top Tier name and logo on their products, retailers must sell only gasoline that meets the Top Tier standards. Many large retailers are in the program, including ARCO, BP, Chevron and Mobil.