NEW YORK --- The price of gasoline has sparked sales of products designed to boost gas mileage, but the federal government warns that these gadgets aren't worth the money.

The products range from devices that fit inside an engine's air intake valve to fuel additives, according to the Associated Press. Manufacturers of these products claim they boost mileage by helping gasoline burn more efficiently. But critics of these products claim otherwise.

"The EPA [Environmental Protection Agency] has tested hundreds of these products," Laura DeMartino, a Federal Trade Commission attorney, told AP. "Even for the few that worked, the gas savings was so small it didn't justify the price."

Nonetheless, consumers are snapping up the gadgets.

"Our sales have probably close to doubled," over the past year, said Dan Baxley, founding partner of Automotive Research Laboratory LLC. The company makes the Vortec Cyclone, which the company claims to boost gas mileage by improving an engine's air flow.

The $40 device fits inside a car's air intake hose, where it "creates a swirling mass like a tornado," Baxley told AP. That creates a finer gas-air mix that burns more efficiently, he said.

National Fuelsaver Corp., which makes Platinum Gas Saver, claims it can improve fuel mileage by 22 percent. The product injects a small amount of platinum into a vehicle's air intake system. The platinum molecules boost the amount of fuel burned by the engine, the company claims, and the remainder is expelled as vapor and burned off by the catalytic converter. Platinum Gas Saver costs $150 for a 30,000 mile supply.

Company owner Joel Robinson said he has been contacted by the FTC and some state attorneys general. But he's been able to defend his product thanks to his victory in an early 1980s lawsuit brought by the U.S. Post Office, which said he was trying to obtain money through the mail by making false claims.

Infomercials for gas-saving gadgets have even made their way on late-night TV, taking up slots previously used by fat-burning belly belts and shiny Asian knife sets.