How Does Heat Affect a Gallon of Gas?

If you’re already hot under the collar over the price of gas, get ready for more pain at the pump now that warm weather is here. Blame simple physics: cold contracts, heat expands. That means you lose at the gas pump when temperatures rise. Here’s why.

The government has standards for measuring gas. According to that standard, fuel should be measured at a temperature of 60 degrees. A change in temperature changes the composition of the gas.

No matter when you buy a gallon of gas, you get 231 cubic inches. But the number of British thermal units or Btus varies depending on the temperature of the fuel. A Btu is the amount of heat required to increase the temperature of one pound of water one degree Fahrenheit or the amount of energy in the fuel.

The gas will expand or contract one percent for every 15-degrees above or below 60 degrees. In other words, the fuel contracts in the cold. So when you buy a gallon, you get more energy for your money. In the heat, just the opposite is true: even though you’re still buying a gallon of gas, you get less energy for your money than you do in cold weather.

A one-percent variation doesn’t mean much when gas is selling for $1 or even $2 a gallon. But it makes a difference when you’re paying $4 or more a gallon.

If you buy 25 gallons of gas at 75 degrees at a price of $4 a gallon, the higher temperature can cost you an extra $1. At 90 degrees, you’ll spend an extra $2. With gas at record high prices, it’s hard to justify spending even a few cents more than necessary for a fill-up.

“Consumers are paying through the nose for gas today, and they’re really angry,” Joan Claybrook, president of the consumer group Public Citizen, said recently. “They’d be even more angry if they realized that $2 billion of what they pay is for fuel that they don’t get.”

Until recently, government regulators thought warm weather fuel losses were offset by fuel gains in the winter. Now that rational is in dispute.

A study in California found that gas holds a year-round average temperature of 71 degrees, well above the 60-degree standard. As a result, consumers in the three largest gas-consuming states–California, Texas and Florida–spend an extra $1.2 billion yearly, it found.

Claybrook and other consumer advocates estimate the expansion of fuel in summer heat could cost consumers nationwide more than $2.8 billion this year, $500 million more than the estimated cost to consumers in 2007.

Big oil companies insist there’s no reason to adjust fuel prices for temperature. But what they’re really saying is there’s no reason to adjust the prices consumers pay at the pump. They already make the adjustment at every other step along the fuel commerce chain.

From the pipelines to the refinery–all the way to the gasoline delivery trucks–temperatures are recorded and prices are adjusted accordingly. The one place the adjustment isn’t made is at the retail level–at the gas pump.

The oil companies say the high cost of retrofitting pumps with temperature sensitive price gauges would simply cost too much. But consider this: those same companies have used the same technology for decades in Canada. They didn’t mind investing in the temperature sensitive gauges there, where colder temperatures put them on the losing end of the equation. They didn’t want Canadian consumers to benefit from gas sold at less than 60 degrees.

Several consumer groups and trade organizations, including the Owner-Operator Independent Drivers Association, an international trade association representing the interests of truck drivers, have thrown their support behind legislative efforts and class action suits demanding automatic temperature compensation at the pump.

Sen. Claire McCaskill, D-MO, filed legislation in Aug. 2007 to phase in temperature-compensation devices on fuel pumps. That bill is currently in the Senate Committee on Commerce, Science and Transportation. Kathryn Vratil, chief Judge in the US District Court for the District of Kansas, is currently presiding over more than two dozen consolidated class action lawsuits filed by consumers seeking similar reforms.

But don’t expect to see changes anytime soon.

So what can consumers do? You can eliminate some fuel loss from evaporative emissions by filling up at night or early in morning, when temperatures are cooler. But that won’t help much as far as gas temperature is concerned. Gas is stored in underground tanks, and the temperature of the fuel in those tanks doesn’t shift much based on the time of day.

One thing you can do is look for gas stations that do a high volume business. It’s likely the tanks at those stations will be refilled more often, so the gas will have less time to heat up to the environmental temperature.

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