The U.S. Environmental Protection Agency has evaluated and reported on the effectiveness of fuel economy retrofit devices for many years. Originally, such products were marketed as emission improvers but with pressures of the oil embargo in the early 1970's most devices began to be promoted to benefit fuel economy. For the most part, such devices are not effective and do not measure up to the claims made by their advertisers. Of over ninety devices evaluated by EPA, only five have improved fuel economy without increasing emission levels. Four other devices modestly improved fuel economy but caused emissions to increase to the point that installation of the devices were determined by EPA to be tampering under the provisions of the Clean Air Act. In general, even those few devices that improved fuel economy were not cost effective.