So-called "hot fuel" provides less energy than a standard 60-degree gallon. Like all liquids at hotter temperatures, fuel expands, reducing the energy content. The hotter the fuel -- whether by radiant heat from the sun or from the refinery process -- the more drivers pay for less energy.

The lawsuit charges the petroleum retailers with breach of sales contract and consumer fraud and seeks relief for motor fuel consumers in the states of California, Texas, Florida, Arizona, New Jersey, North Carolina and Virginia.

Although OOIDA is not a plaintiff, it says it strongly supports the complainants. According to the group's official publication, Landline, it was fuel temperature research by OOIDA Project Leader John Siebert, which led to a famed investigative news series in the Kansas City Star by reporter Steve Everly.

Siebert said that hot fuel has been bilking consumers more than $2 billion a year for decades.

The lawsuit seeks the return of overcharges to consumers and the installation of temperature compensation equipment on all fuel pumps.

Some of those who buy fuel in bulk, such as the U.S. armed forces, already have temperature-adjusted purchase agreements with the oil industry. In fact, fuel is adjusted for temperature all along the distribution chain except at the end point, when it is delivered to individual consumers. With U.S. retail pumps, motorists never know how much energy they will receive from a gallon of motor fuel. By some estimates, retailers are shortchanging drivers 760 million gallons per year in lost energy, the suit alleges.

In Canada during the early '90s, the government gave the nod for output volume adjustment devices for the opposite reason: cold temperatures. Fuel pumps were retrofitted with temperature correction equipment at the oil industry's behest, while in the U.S. "the industry makes more money by not adjusting," Steve Everly wrote in the Kansas City Star piece.

"Automobile travel and small truck traffic will be heavy during this holiday season," said Public Citizen President Joan Claybrook, who participated in a telephone press conference to announce the lawsuit. "This lawsuit comes at a particularly appropriate time to expose a system that has been quietly picking money from the pockets of citizens throughout the country."

The 17 companies charged in the suit are Alon USA Inc., Ambest Inc., Chevron USA Inc., Circle K Corp., Citgo Petroleum Corp., ConocoPhilips LLC, Costco Wholesale Corporation, Flying J. Inc., Petro Stopping Centers L.P., Pilot Travel Centers LLC Inc., 7- Eleven Inc., Shell Oil Products Co. LLC, Tesoro Refining and Marketing Co., The Kroger Co., TravelCenters of America Inc., Valero Marketing and Supply Co. and Wal-Mart Stores Inc.

-- with files from TruckingInfo.com