It's up to each state to make sure you're not getting ripped off at the pump. To see if you are, CBS News chief investigative correspondent Armen Keteyian and the investigative team turned to three reporters at CBS stations to see what they could find.
Mark Greenblatt of KHOU in Houston reports that for the first time ever, the state of Texas is suing a company that runs a chain of gas stations - accusing it of deliberately shorting consumers. The company denies any wrongdoing, but they are not alone. Last year the state found nearly 2,000 pumps at other gas stations that were cheating drivers.
The industry says about 90 percent of pumps pass inspection, and some even deliver a bit more than you pay for.
But a two-month CBS News investigation raises serious questions about whether states even know if drivers are being cheated. CBS News uncovered huge gaps in how pumps are inspected nationwide, including:
As Frank Vascellaro from WCCO-TV in Minneapolis reports, Minnesota doesn't inspect gas pumps annually. There aren't enough inspectors to do it. Of the pumps they were able to inspect this year, 11 percent had problems. The state says stations have to fix them, but only a quarter are ever reinspected. And even though the state can charge operators ripping you off with a crime, that's never happened in Minnesota.
Overall, the investigation uncovered a pattern of inspection that was, literally, all over the map.
Michigan, for example, inspects only after complaints. New Hampshire and Arkansas allow gas stations to hire their own testers, while Tennessee and Florida rely on "statistical sampling."
"Some states are doing very well, others are struggling," said Henry Oppermann, the former head of the Department of Commerce division that sets guidelines for state inspections. "When the inspection period would get beyond, let's say, a year and a half, I think that's really going beyond what regulatory oversight should be."
In fact, CBS News found 17 states allow pumps to go more than a year and a half without inspection.
Among the worst: Arizona, at every three years. Maine's inspections are up to every four years. Same with Texas. One pump CBS News found in Fort Worth, Texas, was last inspected in 2003, when gas was $1.56 a gallon.
Speaking with Oppermann, Keteyian said: "I gotta tell you something, I don't have a great deal of confidence right now ... that I am actually getting what I am paying for."
"When there's a lack of oversight, there's a potential - a greater potential for abuse," Oppermann said.
And even when pumps are regularly inspected, that's no guarantee.
Anna Werner at KPIX in San Francisco found that in California, 94 percent of pumps pass inspection. But consumers can still be cheated. That's because pumps can pass even when they dispense a little less than what the pump says. It's a margin of error the law allows.
So a high-volume station that routinely sells a little less than a gallon could rake in around $50,000 a year extra - for gas you never get.
"Shame on them!" one driver said. "That's all I can say, shame on them."
Is it time for Congress to look at this as a national issue?
"It would be beneficial to have a national coordination of efforts," Oppermann said.
Not likely. When CBS News tried to find out the last time Congress looked into the problem, but came up empty. Fact is: it never has.