In 2004, a consortium of major auto-makers — BMW, General Motors, Honda, Toyota and Volkswagen / Audi — came up with "Top Tier Detergent Gasoline Standard" to gasoline brands in the US and Canada that meet their minimum standards for detergent content and do not contain metallic additives. Top Tier gasoline contains higher levels of detergent additives in order to prevent the build-up of deposits (typically, on fuel injector and intake valve) known to reduce fuel economy and engine performance.