Consumers are feeling the pain at the pump, as gas prices have risen for nine straight weeks. Now lawsuits around the country claim drivers are being ripped off in a gas gouge they can't even see.
There are at least nine lawsuits pending that claim some gas stations are padding their profits by selling warm gasoline.
That might sound strange, but think back to high school physics. Liquids expand as they get warmer, so if the gasoline at the pump is overheated, you don't get as much in your tank.
Mark Rushing is a long-distance trucker. When he fuels up, every penny counts.
"Fifty-eight gallons of gas cost me $168 dollars," Rushing said.
But he says he often overpays because gas stations don't follow the fuel industry's own standard that gas should be sold at 60 degrees Fahrenheit.
When the temperature outside gets above 60, gasoline at the pump expands, and you get less of it.
Physics professor Michio Kaku demonstrated the concept by heating water in a bottle. As it heated up, it expanded and overflowed. In other words, it took less water to fill the same size container.
"Remember that gasoline expands roughly three times faster than water," Kaku said. "So magnify this effect inside your gas tank."
You pay the same, but you're getting less energy for your car. That's why Rushing and other drivers are suing. They say they're being ripped off because pumps don't account for outdoor temperature changes.
It's something most people never even think about.
"I just never thought about it. I put gas in my car and go," said Linda Morton.
An investigation by the Kansas City Star newspaper found that American drivers may overpay $2.3 billion a year, with drivers in warm states like California hit the hardest.
An independent fuel marketers and retailers group argues if any gasoline is lost, the amount is tiny.
"We do not see the information they have gathered as being credible," Jay McKeeman said. "Basically it's about a tablespoon in 12 gallons of gasoline."
But consumer advocates point to chilly Canada, where the pumps are controlled for outside temperature. The industry went along with it there, and cynics say that's because fuel "shrinks" when it's cold, which benefits consumers.
"They fixed it in Canada because they [the industry] were losing money," said trucker Mark Rushing. "How come they won't fix it here?"
There are no laws requiring gas stations in the United States to adjust for hot fuel, so they are not doing anything illegal.
But if you want to avoid "losing" fuel in your tank, fill up overnight or early in the morning before it gets hot.
Or fill up if it's below 60 degrees -- you may actually get a little extra fuel for your money.