“If the pump was off a penny or two, it would make a difference of $10 to $20 a week,” said Roger Auffet, a fuel device safety inspector for the Missouri Department of Agriculture.

Auffet spends his days pumping gas at stations in Greene County.

“I pull five gallons of every product on every pump,” he said.

He tries to make sure someone gets a gallon of gas when he pays for a gallon.

“It’s hard for them to know what meters are doing without us coming around,” said Auffet.

State law requires all pumps to fall within 6 cubic inches of five gallons.

“Five-thousandths of a percent is all they’re allowed to be off,” said Auffet.

Despite these stringent guidelines, it's rare for pumps to be inaccurate. Auffet tests them twice a year. That's nearly 9,300 in Greene County since the beginning of 2007 -- and just 187, or about 2 percent, have fallen above or below the 6-cubic-inch tolerance.

KY3 News obtained copies of all 187 of those out-of-compliance inspection reports to see how much consumers lost -- or gained -- as a result. The reports show more than two-thirds of those that measured inaccurately were in the favor of consumers.

In the most extreme case, in April, the Cody's store in Republic was giving away a gallon and a half per five gallons that were pumped.

“One of them got hit by lightning,”

A company representative confirmed the mistake was a result of storm damage -- and the pumps were put out of service until they were fixed within days.

On the other side of the spectrum, the most a pump measured under its meter reading was 25 cubic inches. Even in these worst cases, that only translates to about a penny per tank.

On average, when pumps in Greene County measure out of tolerance, it's by about 10 cubic inches -- or a half a cent per tank.

Another problem that inspectors find from time to time is what’s known as creeping. The pump trigger is off but the price still increases. This happens rarely but the inspector will put the pump out of service until the problem is fixed.

The inspection reports show just three cases of creeping since the beginning of 2007. All were fixed within days.

As far as the most frequent inaccurate pumps, 35 percent of the pumps at Travel Centers of America in Strafford were out of tolerance during an inspection in June -- but all were in the favor of the customer. The store manager there says the store had just changed over from manual to electronic calibration when they were tested. Again, all were fixed as quickly as possible.

Pumps that measure between 6 and 12 cubic inches off five gallons – either up or down -- get to stay in service but Auffet re-inspects them within two weeks. Pumps that measure 13 cubic inches or more off five gallons are immediately put out of service until they're fixed.

If pumps out of tolerance are rare, Auffet says cases of stations purposely causing them to pump too much or too little are all but nonexistent.

“It’s almost impossible for them to know that,” he said.

Despite what the reports show, many consumers are still skeptical. Auffet feels their wrath through the sheer number of complaints.

“I used to get two a month; now I’ve been getting two a day,” he said.

Of the complaints about inaccurate pumps that Auffet received since the beginning of 2007, he says just one was valid. He says the pump was off by so little that there’s no way the consumer could have known it. Still, he visits every station that receives a complaint.

If you'd like to see how gas station did during its inspections, we put all the out-of-compliance inspection results online.