Once largely limited to relatively expensive low-production high-performance cars because of higher cost than carburetion, fuel injection has become increasingly used on cars throughout the world. In the U.S., the primary driving force has been easier control of exhaust emissions and improved fuel economy. However, deposits formed in the delivery area of the injector can reduce fuel economy and increase emissions. Tests have shown that some gasoline additives can clean up injectors and keep them clean. These additives also improve carburetor cleanliness.