The Science of Summer Gas Gouging

August 14, 2007: Source – Alternet

hot summer gas pump

Should Americans demand that their fuel dollars buy a season-neutral measure of energy, like our Canadian neighbors?

It might not surprise you that the people who brought you refinery shutdowns during supply crunches are resisting the use of a device that would make it so. In an era of record profits, Big Oil doesn’t want you to know how many molecules go into your tank.

As reported by Brian Beutler in Alternet:

A gallon of gasoline contains a certain number of molecules, which combust in your car’s engine to provide it with energy. If you heat up that gallon of gasoline it will expand, leaving you with a larger volume of gas than the gallon with which you started. But your new volume will contain the same number of combustible molecules and therefore will provide the same amount of energy as it did prior to the heating. That means a tank full of “hot” gas will provide a car with less energy than will the same tank full of “cool” gas, which is why you’ve probably been advised (correctly) not to buy gasoline when it’s hot outside. Simple, right?

It is if you live in Canada, at least. There, gasoline retailers install metering systems in their pumps to determine how much the fuel they sell has cooled or heated from its standardized refinery temperature, and then adjust the price accordingly. If the fuel has become warmer, it also becomes cheaper. If it has cooled, it becomes more expensive. Which is to say that Canadians — to a greater extent than Americans — pay for the energy they get out of the gasoline and not for the volume of liquid fuel they purchase.

Maybe we should be glad that summer heat literally inflates gasoline. Higher gas prices (adjusted for a mythical “driving season”), in combination with this physical phenomenon, could help some drivers reconsider fuel economy. After all, summer is when air pollution intensifies as heat keeps exhaust-produced ozone at ground level.

But wait. Beutler goes on to point out that:

The idea of correcting price for temperature has deep roots in the industry: oil companies have done so for gasoline wholesalers for nearly a century. The only ones in the North American energy chain who pay by volume rather than by energy value are U.S. consumers.

Two or three cents a tank certainly doesn’t matter to an individual consumer. But it adds up to $2 billion a year for the oil companies. If they don’t want to bother with the thingamajig that adjusts price for temperature-related expansion, don’t force them to. Simply have them pay those monies directly into a fund dedicated to rebuilding our crumbling infrastructure—or better yet, redesigning the infrastructure for the kind of mass transit, bicycle, and pedestrian travel that contributes to reduced emissions and less dependence on fossil fuel.


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  • Scott M.

    The pumps in Canada are set to read out what the volume of gasoline would be if it was delivered at Normal Temperature and Pressure (20C/68F, 101.325kPa/1 atmosphere).

    If they actually changed the *price*, there’d be no way to tell amongst the daily swings of price and would be eaten by the gas companies.

    What this means is that you take appears to take 53L in the summer, 60L in the winter. Very few people notice (or care) though. If miscalibrated though, either the retailer or consumer could be left at a disadvantage.

  • thinkerbelle

    But volume affects price. Not of the individual measure, but of the entire tank.

    Today a litre is $1.019 in White Rock, and I only pay for 53L to fill the tank. That’s $54 for gas that will take me 500 miles down the road. In the US, pretending that we found a place that sold the same day at the same price (and in litres), I’d be charged $61.14 for the same tank.

    It’s not exactly price that’s adjusted, but it sure has an impact on the pocketbook.

  • Scott M.

    That’s why I said “Not Quite”. The article is a little misleading, it makes it sound like the posted price magically drops on a hot day.

    Thank goodness it doesn’t! No doubt the gas companies would take advantage of that, and it would be hard to tell if the price was really going up or not. The volume adjustment is a much fairer method and is clear to both the retailer and the consumer (if he or she cares to look into it).

  • Jerry

    Interesting article. It just reinforces the fact that if we had more efficient cars the volume would be less.

  • rocknerd

    the gas is stored in underground tanks where temperature is pretty much constant. I have trouble believing that such a large volume of gas buried underground would fluctuate in temperature on a daily or even seasonal basis. Has anyone documented this?

  • Jeff

    All this over a situation that already corrects itself is mind blowing. Even though I get a better theoretical deal in the winter on gas my milage is much worse due to the colder temperatures so I do not see the benfit of lower gas prices. In the summer when I am getting “fleeced” for a few cents my car is much happier and goes farther on a gallon of gas so the loss is all in our attitude not in reality. I say tax the #$%! out of gas to provide money for the things we should be spending money on “redesigning the infrastructure for the kind of mass transit, bicycle, and pedestrian travel that contributes to reduced emissions and less dependence on fossil fuel.”

  • Stan

    If we overpay per molecule in the summer when it’s warmer than standard, we underpay in winter when it’s colder than standard. Since Canada is colder more often than it’s warmer, adjusting to the standard actually helps the oil companies more often than the consumers; it eliminates the underpayment during the cool seasons. I would bet that over an entire year many Americans actually get a net savings by not adjusting, especially in the northern parts of the country.

  • Van

    It appears that if you pump gas that is colder than the standard you put more energy into your tank for the same money. Thus it would be in the interest of the retailer to correct for temperature. But if you pump gas that is warmer than the standard, you put less energy into your tank than you pay for. Thus it would not be in the interest of the retailer to correct for temperature.

  • Cameron

    As noted by several postings Gasoline is stored underground and is therefore cooler than ambient air temperature in the summer and warmer in the winter… pretty much has to average out. The ambient air temperature is irrelevent since the gasoline doesn’t have time to reach it on the short trip from underground tank to gas tank.

    Even if it did matter it still wouldn’t be worth it. These devices that make purchasing fuel ‘fair’ for the customer is hardly that. For one thing they cost thousands of dollars which must be recouped by the gas station owner… in other words, they have to charge more.

  • pprius2006

    Just before midnight, when the air temperature of 10.0°C, Karl stops and fills the 0.0600 m3 gas tank in his car. At noon the next day, when the temperature has risen to 32°C, Karl finds a puddle of gasoline (βgas = 3 x 10-4 C°-1) beneath his car.

    How much gasoline spilled out of Karl’s car? (assume that there was virtually no change in the volume of his tank)