PHOENIX More fuel pumps in California and Arizona are getting labels warning that the energy content of fuel varies with temperature.

ExxonMobil is now posting small informational decals at all of its company operated and company owned-dealer operated stations in Arizona and California to advise customers of the measurement basis, said Prem Nair, a company spokeswoman.

"It is simply a reminder that the dispenser sells motor fuel by volume," Nair says.

The decals on the pumps are called a "Motor Fuel Measurement Notice." It reads: "This device dispenses motor fuel by volume measured in gallons. It does not adjust the volume for variations in the temperature of the fuel. The temperature of motor fuel affects the energy content of each gallon dispensed."

Oil refiner Tesoro initiated the sticker effort at its California stations, including the USA Petroleum chain and more than 250 Shell stations recently acquired by the company. (See Aug. 15 Bus & Motorcoach News.)

Meanwhile, a U.S. senator has introduced a bill that would require fuel pumps to have automatic temperature-compensation devices.

Fuel expands as its temperature rises, but is sold by volume at the retail pump at a benchmark of 60 degrees. Elsewhere in the supply chain, fuel is sold temperature-adjusted, meaning slightly more gasoline and diesel are provided at higher temperatures.

National Association of Truck Stop Operators spokeswoman Mindy Long said she knows of no plans to label diesel pumps among its member truck stops and travel plazas.

While NATSO has no position on the labels, the association is against mandatory temperature compensation devices, Long said, saying the expense of installing and monitoring the more sophisticated pumps would be passed on to fuel buyers. NATSO is seeking an independent study done of the economic and scientific effects of temperature variation.

U.S. Sen. Claire McCaskill, D-Mo., proposed legislation last month that would require the installation of automatic temperature-compensating equipment in new and upgraded retail pumps within six years.

The Future Accountability in Retail Fuel Act would provide assistance for retailers to comply -- $1,000 per pump, but no more than $10,000 per retailer -- and impose penalties on those that don't. The bill, S1997, has been referred to the Senate Commerce, Science and Transportation Committee.

The Owner-Operator Independent Drivers Association, based in McCaskills home state, has endorsed the legislation, as has Public Citizen, Consumers Union, the Foundation for Taxpayer and Consumer Rights, the Consumer Federation of America and the U.S. Public Interest Research Groups.

In Arizona, where the so-called hot fuel issue is heating up, so to speak, the state Department of Weights and Measures has begun taking fuel temperatures at stations to get a 12-month average.

Already it has found summer fuel temperatures of about 104 degrees. Based on that finding, Phoenix-area motorists are paying about $1 more for a 15-gallon fill-up than they would for the same amount of energy if the gasoline were 60 degrees, the industry standard.

That figure rises when fuel prices hit the $3 mark they saw earlier this summer.