Gas prices are painfully high, and now some customers are told they can improve their mileage right at the gas pumps.

At one Sanford gas station, there are more options than regular or premium. At the pump, there's a device that shoots a fuel additive right into your tank that's supposed to boost mileage by nearly 10 percent.

The company is Additech, and the devices are turning up at Murphy USA stations.

Action 9 found curious customers and downright disbelievers.

The machine pumps a "good mileage" blend for an extra $2, "better mileage" for $5 and a "best mileage" boost for $8 a tank.

The company said it removes carbon buildup to increase mileage and reduce emissions.

When gas prices increase, the sales pitches for fuel boosters soar, too, but this is the first to hit you right at the pump, a place where you could be most tempted to stretch a tank of gas.

"I can't image how that's real," said Jay Zembower, who is a master mechanic and car repair expert, in court.

Zembower thinks some additives improve overall performance, but he has never found one that actually increases mileage like that.

"That's what I would consider a snake-oil claim, any claim like that," said Zembower.

AAA issued a warning when the product showed up in the Carolinas, saying it's more about marketing than boosting mileage.

Additech told Action 9 its additives are made by Afton Chemical and that testing showed mileage improvement. Additech said more than 3 million customers a year use its product.

AAA Florida told Action 9 fuel additives are not big mileage boosters and that better driving habits and good maintenance are better options.

Murphy USA did not respond to Action 9's request for comment.