With gas prices on the rise, who wouldn't want to cut costs? But can a device that plugs into your car's power outlet really improve your gas mileage by 25 per cent?

The television commercial for the Fuel Doctor's FD-47 promises to help "optimize your engine's speed, timing control, and fuel injection."

The FD-47 ad goes on to claim that its "fuel-efficiency booster" creates a more stable current, resulting in increased power and improved fuel economy.

It says "certified lab and field tests show increased MPG of up to 25 per cent."

Consumer Reports wanted to see just how well the $50 Fuel Doctor FD-47 works.

"It claims to have the best effect on vehicles older than two years. And also claims to have some effect on vehicles that are newer," the magazine's David Champion said.

Consumer Reports tested the Fuel Doctor device in 10 different vehicles. Six of the cars were equipped with a highly-accurate fuel economy meter. Testers then measured fuel efficiency for both city and highway driving.

The other vehicles were put through acceleration tests, to see if the Fuel Doctor device increases power as claimed. Then the tests were repeated without the Fuel Doctor. So in the end?

"We found it made no significant difference at all. The only thing we saw, the light was on," Champion said.

Consumer Reports says several things will improve your mileage:

• Avoid fast accelerations and braking hard.

• Watch your speed.

• Do regular maintenance on your car.

• And keep your tires properly inflated.

In the past, Consumer Reports has tested bolt-on devices that claim to give you big improvements in fuel-economy including the Fuel Genie, Platinum Gas Saver, and Tornado Fuel Saver. But Consumer Reports has yet to find one that makes a significant difference.

With a report from CTV British Columbia's Chris Olsen