And that means Utah drivers who fill up during the summer may get fewer miles out of a tank of gas than during the colder months, when the temperature of the fuel they pumped into their automobiles and pickups was lower.

The prospect that motorists may not always be getting all the energy from each gallon of gasoline that they paid for has ignited a growing controversy across the country.

And this week it resulted in the filing of a proposed class action lawsuit in the U.S. District Court for Utah that will attempt to hold companies such as Flying J, Sinclair Oil, Exxon Mobil, Chevron, Shell and ConocoPhillips responsible for selling "hot gasoline" to motorists in the state.

"This is a serious problem, especially with truckers" whose livelihoods are tied to the cost of fuel, said C. Val Morley, an attorney in American Fork who filed the proposed class action lawsuit. "Similar lawsuits have been filed in other areas of the country."

About 100 years ago, federal regulators determined that a gallon of gasoline would be 231 cubic inches of fuel measured when it was 60 degrees. And it is that 231 cubic inch per gallon standard that is used on gasoline pumps in Utah and across the country.

When a gallon of gasoline is 60 degrees it exactly will fill a one gallon container. But that same gasoline at 90 degrees would spill over the sides of the container. It is that spillage that represents the energy drivers allegedly paid for, but didn't get, when they purchased a gallon of "hot gas."

The Utah lawsuit contends that hot gasoline is costing American motorists a couple of billion dollars a year and drivers in this state millions annually. And it contends that money represents excess profits for the big oil companies.

Morley also points out in the lawsuit that the petroleum industry in Canada put "temperature compensation equipment" on most retail pumps in that country because there the problem is "cold gas."

"Where the sales of hot motor fuel, as in the United States, allow the petroleum industry to earn even higher profits, the industry opposes the installation of such equipment as being too costly," Morley wrote. "Where the sales of cold motor fuel, as in Canada, reduces industry profits, the industry supports the use of such equipment."

Sinclair Oil spokesman Clint Ensign said the company hasn't yet received a copy of the lawsuit and therefore couldn't comment. "I will say that we are in full compliance with the way the state of Utah requires us to dispense fuel."

Calls to Flying J and Chevron were not immediately returned.

And not everyone agrees that hot gas represents a big problem.

Larry Lewis, spokesman for the Utah Department of Agriculture that oversees the state's Division of Weights and Measures, said while the temperature of the motor fuel sold in this state may fluctuate season to season, it likely evens out over the long run to around 60 degrees.

If the controversy gets addressed it likely will be on the state level, said John Bisney, spokesman for the American Petroleum Institute, a trade organization representing the nation's oil companies.

"We're not aware of any state that has addressed [fuel] temperature compensation," Bisney said.

He said that states frequently take their cue on such questions from the National Conference of Weights and Measures. "And they apparently plan to vote in July on proposed model legislation that each state may want to consider."

The proposed Utah class action lawsuit wants the oil companies to install temperature correcting equipment on their retail motor fuel pumps or post notices to consumers that the energy of the fuel they are buying varies due to temperature.

And it also asks the court to award each class member the amount of actual damages they suffered or $2,000, which ever is greater.