Top Tier detergent gasoline standards set minimum acceptable levels for control of deposits on intake valves, fuel injectors and combustion chambers and for intake valve sticking at cold starts. Designation as a Top Tier gasoline retailer requires that all grades of gasoline sold by a retailer meet Top Tier detergent gasoline standards established by seven major automakers, including General Motors, Honda, Toyota and Volkswagen. As well, gasoline sold at all outlets carrying a retailer's brand must also meet the standards.
Top Tier gasoline contains extra cleaning agents, about twice the amount required by the U.S. Environmental Protection Agency, according to Marie Valentine of the Toyota Technical Center, and cannot contain metallic additives. Top Tier gasoline is noted for keeping engines running better and longer, while helping to ensure that vehicles meet emission standards. As of 2015, there are 30 Top Tier gasoline retailers in the United States, including Costco Wholesale, Chevron, Exxon, Phillips 66 and Valero. One U.S. retailer, 76, reports that it exceeds Top Tier standards by 30 percent. Technical specifications for each of the Top Tier standards and testing methods are available at TopTierGas.com.
While opinions vary about the benefits of Top Tier gasoline, experts agree that the build up of deposits inside a car's engine can lead to poor performance and increased emissions.