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Your gas tank may not be as full as you think

A "gallon" may actually be less on hot days.

By CURTIS KRUEGER
Published June 4, 2007

If you're frustrated about how much a gallon of gasoline costs these days, wait until you hear this: You may not be getting a full gallon.

It's a simple matter of geography and physics. When you heat a liquid, it expands. A full container of gasoline that's 90 degrees actually packs less energy than a full container of gasoline that's 60 degrees.

We live in Florida, a hot state. So it's quite possible we're pumping warmer gasoline, and getting fewer miles for our gallons than drivers in Minnesota, where gas is likely to be cooler.

And this is why the price of gas may soon be adjusted for temperature. It's an idea that some say would provide much-needed relief to consumers. Others argue it would create a messy and expensive layer of government regulation.

"The fact is that we should have a fair system where the pumps adjust to the temperature so you get the full measure of what you're paying for," said Joan Claybrook, president of the national group Public Citizen, which has been active on this issue, adding, "The warmer the state, the warmer the fuel, the more you lose in terms of the fuel content."

Time for a vote

A group called the National Conference on Weights and Measures will vote this summer in Salt Lake City on a proposal for adjusting the price of gasoline and diesel fuel according to temperature. If the group votes yes, it could ultimately change the way individual drivers buy gasoline in Florida and other states.

Under this plan, states could allow gas stations to adjust gas prices to account for temperature. If the gasoline is warmer than 60 degrees Fahrenheit, you'd get a discount. If it's cooler than 60 degrees, you'd pay more.

The downside is that the voluntary method could be confusing, especially if some stations sell gasoline one way and some sell it the other way.

"I don't know how the public is going to trust what they're getting," said Jim Smith of the Florida Petroleum Marketers and Convenience Store Association.

"Going to this does not guarantee any lower retail prices," Smith added, "although I wish it did."

Gregg Laskowski, a spokesman for AAA, also predicted it would be difficult to explain the temperature-adjusted system.

"I think it would be a tremendous challenge to try to present all of this information in a way that consumers can not only understand but agree with. It's our nature to be skeptical."

Claybrook said she thinks mandating the new system would be a less-confusing and fairer method. But she said the voluntary approach now under consideration would be a step in the right direction.

Those pennies add up

The difference between warm and cool gasoline is not huge. The Kansas City Star, in an extensive article last year, used this example:

Say your car has a 20-gallon gas tank and gets 20 miles per gallon, and it's filled with gasoline that was 60 degrees when you bought it. The car would go 400 miles on that tank.

Now let's say you fill the car with 90-degree gasoline -- in other words, warmer, expanded gasoline. Now you would go 392 miles on a full tank, 8 miles less.

The difference would amount to mere pocket change each time you fill the tank with warm gasoline. But as all large businesses and governments know, pennies add up. The Star estimated Floridians were overspending by $367-million a year by buying warm gasoline.

Smith disagrees with those numbers. But the final decision on what to do may be in the hands of consumers.

Owners would decide

If the National Conference approves the proposal this summer, the Florida Department of Agriculture and Consumer Services will have authority to implement it in this state. If that happens, it will be voluntary -- gas stations and companies could sell gasoline that way if they wanted to, but wouldn't have to.

Gas stations will sell gasoline adjusted for temperature differences "when consumers demand it and should not be required to do so before then," a committee of the National Conference said.

Whether consumers will get that chance should become clearer after the vote this summer.

Curtis Krueger can be reached at ckrueger@sptimes.com or 727 893-8232.

[Last modified June 4, 2007, 00:33:15]