High Quality Content by WIKIPEDIA articles! Top Tier Detergent Gasoline is a designation given by a consortium of major automakers--BMW, General Motors, Honda, Toyota, and Volkswagen/Audi--to gasoline brands in the U.S. and Canada that contain prescribed levels of detergent additives and do not contain metallic additives. Top Tier gasoline contains higher levels of detergent additives in order to prevent the build-up of engine "gunk," known to reduce fuel economy and engine performance, and possibly lead to mechanical breakdown. The Top Tier designation is separate from the issue of octane levels--in order to get the designation, gasoline companies must include the minimum prescribed levels of detergent additives in all grades of gasoline they sell, whether it is economy (low-octane) or premium (high-octane). However, premium gasolines may contain even higher levels of these additives. To date, 30 gasoline companies offer Top Tier gasoline, and it is freely available throughout the US...