CLEVELAND -- NewsChannel5 chief investigator Duane Pohlman explained how the oil industry "cheats" consumers out of gasoline in the summer.

The investigation of hot fuel is already triggering hearings in Washington, Pohlman reported.

Truckers began reporting the problem years ago when they noticed their mileage plummeting every summer.

John Siebert, with a truck drivers association that has 50,000 members, investigated the fluctuations and stumbled on the oil industry secret.

"You're paying more and you're getting less energy in each gallon," Siebert said.

It's called thermal expansion, or hot fuel. In the summer, gas heat up and expands, so much so that the weight of a gallon of gas actually goes down by 1 percent for every 15 degrees.

This means you're actually getting less than a gallon when the fuel is hot.

One study found American consumers are being cheated out of $2.3 billion a year. Another study found people in Ohio are being cheated out of $34 million at the pumps every year.

"Summertime is a perfect storm every year for this to happen because the prices go up and the temp goes up at the same time," said Siebert.

While the oil industry has known about hot fuel for 100 years and even adjusts the price it sells internally by the temperature, in the U.S. it has done nothing to compensate consumers.

In Canada, special pumps measure the fuel's temperature and adjust the price. With Canada's colder temperatures, that favors the oil companies.

Rep. Dennis Kucinich, D-Ohio, said he has had enough.

"I mean, why should people be paying for gasoline they're not getting? It's cheating," he said.

Kucinich, who chairs the congressional subcommittee on domestic policy, is holding a special hearing in Washington on Friday, demanding that oil companies compensate consumers for hot fuel.

"It is absolutely urgent that somebody stands up for the consumers and tells the oil companies, 'Look, it's over,'" Kucinich said.

According to Kucinich and critics alike, the issue of hot fuel is about to trigger a heated debate on Capitol Hill.