The Federal Trade Commission published a report in September 2006 stating that consumers should be wary of products that are alleged to improve fuel economy. None of the 93 products tested by the EPA actually improved gas mileage. The FTC lists both mechanical devices and liquid additives. Testing took place at the Ann Arbor, Mich., labs of the EPA over 30 years. Ten of the devices did show small improvements in fuel economy, but not what was advertised. Four of those 10 increased emissions.