Escalating fuel costs might not be the only culprit. You could be getting tricked by the pump.

"When it says it's dispensing 5 gallons, are you really getting 5 gallons?" said Alan Rogers, program manager for the Virginia Office of Product and Industry Standards. "We make sure when you purchase 89 octane, you get 89 octane."

The good news, according to Rogers, is that most mistakes actually benefit the customer.

"With a majority of pumps, the error is in favor of the consumer," Rogers said.

His division of state government must inspect every gas pump in the state at least once a year. If a pump fails to meet any standards, they return to reinspect.

John Bates, inspection supervisor for the region that includes the Fredericksburg area, said there is a low occurrence of failed pumps--about 9 percent compared to the state average of 10 percent. Bates declined to discuss findings at specific Fredericksburg-area stations.

There are about 3,000 pumps in Fredericksburg, Stafford and Spotsylvania.

With 3 percent of pumps, the amount or type of gasoline dispensed is the problem. Many times, it is something more trivial.

"This industry is very highly regulated," Bates said. "It's not a regular practice that we find. I've never seen anyone tampering."

But tampering does happen.

David Lazier, chief of the California division that oversees gas pumps, said an investigation there led to about 30 stations being busted for duping customers. Investigators in other states have unearthed similar fraud.

In California, some stations were using equipment that tricked customers into believing they were getting more gasoline.

"We do have a certain faction that feels they need to make an illicit profit," he said.

The gas dealers were especially difficult to catch there because the equipment initially fooled inspectors. While inspectors usually pump 1, 5 or 10 gallons of gasoline for testing, the illegal equipment ensured those amounts dispensed properly.

"They were using our own test methods to beat us at our own games," he said. "We started receiving enough complaints to lead us to believe something was going on."

When undercover inspectors pumped differing amounts of gasoline--such as 6 or 9 gallons--they discovered they were shortchanged by as much as a third.