WASHINGTON, D.C. — Truck drivers and motorists in seven states filed a complaint recently against 17 oil companies and gasoline and diesel retailers for overcharging at the pump for fuel heated above the industry standard.

This hot fuel provides less energy than a standard gallon and bilks consumers of more than two billion dollars nationwide, according to information released during a news conference to announce the lawsuit.

Like all liquids, the volume of fuel expands and contracts when the temperature changes. Hotter fuel has less energy in each gallon than cooler fuel. Regardless of whether fuel temperature rises due to radiant heat from the sun or the refinery process, the results are the same: less energy.

Those who buy fuel in bulk, such as the US armed forces, have temperature-adjusted purchase agreements with the oil industry. In fact, fuel is adjusted for temperature all along the distribution line except at the end point, when it is delivered to individual consumers. By some estimates, retailers are shortchanging drivers 760 million gallons per year.

Although the industry claims that the cost of hot fuel amounts to pennies for individual consumers, it really adds up to a $50 tax on every car in the country, said John Siebert, project manager of the Owner-Operator Independent Drivers Association (OOIDA).

But the oil industrys opinion about temperature-adjusted motor fuel pumps at the point of retail sale depends on where it is standing. While it opposes temperature compensation in the US, it embraces it in Canada, where it stands to lose money from selling cold fuel that has more energy than the standard gallon.

The industry has voluntarily implemented the use of temperature control equipment at retail pumps in Canada and supported legislation there to make the technology mandatory at the point of sale.

Ultimately, Congress needs to protect US consumers against the industry-wide practice of hot fuel overcharges but in the absence of government protections, the only solution is for consumers to band together and force a remedy through the legal system, said Joan Claybrook, president of Public Citizen.

The class-action 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. It calls for remedies in the form of restitution and the installation of temperature correction equipment for pumps that dispense gasoline and diesel fuel. The seventeen companies charged in the suit are Alon USA, Ambest, Chevron USA, Circle K, Citgo Petroleum, ConocoPhilips, Costco Wholesale, Flying J., Petro Stopping Centers, Pilot Travel Centers, 7-Eleven, Shell Oil Products, Tesoro Refining and Marketing, The Kroger Company, TravelCenters of America, Valero Marketing and Supply Company, and Wal-Mart Stores.