Why Is The 9/10ths Necessary When Buying Gas?

Yesterday, I was filling up some premium gas at a premium price, and began wondering why the heck they add the 9/10ths to the end of it?  If the oil companies need that extra penny, just take it! Why do they need to bring fractions into my happy fraction-free lifestyle?  Considering that they add a buck (or more) per gallon to the price of gas every summer anyway, I just don’t see the need for the extra 9/10ths of a cent.  Is this something that was a really great idea in the 1920’s when a penny was a big deal?  Or maybe it’s a conspiracy designed by high school math teachers to make us think that fractions are used “in the real world”.  Of course I don’t want to pay more than I already do for gasoline, but that fraction really cramps my style when I’m pumping my fuel.  Did I miss the day in school when they explained why this insanity exists?  Is it common knowledge?  Somebody help!

19 comments to Why Is The 9/10ths Necessary When Buying Gas?

  • Curtis

    The fuel companies are technically not charging you an extra 9/10ths of a cent. The are charging 1/10th of a cent less. This is because the true volume of gas you pump is a little less due to evaporation of vapors or fuel that never makes it to your tank. Somewhere, someone who's much smarter than I figured out that 1/10'th of a cent is what those vapors would cost you.

  • Curtis, you are at the top of your game with the gasoline facts! Is this common knowledge (that I'm clearly missing) or are you "in the know"? ;) I guess I do feel a little better knowing that they aren't trying to grab an additional penny from me. I do still think fractions crowd me while pumping fuel though!

  • Steve Curcuru

    Hi Jeremy,

    It's *also* due to the same reason that store prices are always $3.99, (which is just a decimal fraction, after all) and not $4 – marketing experts know there's an inherent psychological bias to weight the $ figure more than the cents in buying decisions – hence, you'll always tend to reach for the $3.99 item over the $4 one.

    Love your blog – keep up the good work !!

  • Thanks for the kind words Steve!

  • Nick


    That doesn't make any sense… .if 1/10 of a cent was lost in vapors when gas was only say .50 per gallon wouldn't the cost of the lost vapors be like 5/10 of a cent now. I think Steve is closer to the truth.

  • Tom

    If it was once inteneded to allow for evaporation, it isn't anymore. That thinking would be "by the gallon" (volume) and would fluctuate with the price of gas…a lot more than 1/10th these days!

  • JohnEd

    No, it's the volume of kinda fuel stuff…the other tenth is H2O. and you thought it was about $$$.

  • Oldgriz

    All your theories on evaporation and conspiracy are uninformed speculations.

    Let me educate our family here. Contrary to belief the penney IS NOT the smallest denominator in our currency ! The "MILL" is there are 10 (ten) Mills to a penny ! The mill has never been removed from use but is no longer in use. Also The term E Pluribus Unum, is incorrect It should be Et Pluribus Unum. We can put a man on the Moon, but we can't spell and don't know our own History..

  • Oldgriz

    By the way This is not an April fools joke do your home work and find out

    PS: search the dictionary Webster etc..

  • len

    if the fuel vapor theroy was correct ,we should get more than the 1/10 of a cant .all gas stations have a fredally mandated VAPOR RECOVERY system installed on their pumps,so that means they are recovering vapor and are reselling them again right?

  • deadwhale

    The 9/10 has to do with tax.

  • anonymous

    My question is more of a mathematics…
    Why a fraction? $2.89 9/10 is the same as $2.899
    Is decimal number so hard to understand for Americans?
    Verizon doesn’t know the difference between .002 cents and .002 dollars. http://science.slashdot.org/article.pl?sid=06/12/09/0625245

  • anonymous

    Here is an examples of gasoline prices in Europe. Notice that there still the tenth of a cent but no fraction…


    While looking for pictures, I found this cartoon that mixed the decimal with the fraction.


    A tenth of a tenth of a cent???

  • David

    That’s not a decimal mixed with a fraction. Those are whole numbers in the thousands (hence the humor behind the joke; those prices are appropriate for a cheap car in the States). The commas just make them easier to read. If they were decimals, they would be periods, not commas.

  • Andrew


    E Pluribus Unum is indeed correct, but slightly contracted. If one were to spell it out, it would be Ex Pluribus Unum –> out of many, there is one. The Latin motto refers to the creation of a single nation out of many colonies/states.

  • Frank

    Andrew is correct. “Et” is Latin for “and,” “e” is shortened from “ex,” meaning “from”. If it were “et” and not “e,” the word “pluribus” wouldn’t make sense; Latin is an inflected language, and the word endings denote the meaning of the word in the sentence. Oldgriz, before you start claiming that can’t spell, maybe you should try doing a little research. Interesting fact about mills though, I didn’t know that ;)

  • mike bentley

    Whatever it is guys, we’re still getting ripped off. I wish their surplus would build to the point they’re swimming in gasoline with no sales.
    Yeah. let’s all not buy any gas for a couple days all at the same time. that’ll get ‘em squealing. Yeah right.

  • Matt

    For the Americans who think they pay too much for gasoline, here’s a photo I took a few years back in Italy: http://i95.photobucket.com/albums/l122/scibamb/eurogas.jpg

    €1.245 per liter is roughly $6.50 per gallon.

  • Tony

    Matt, maybe they charge so much in Italy so they can keep replacing the gas hoses that are always damaged by the customers autos. Appears that they get ran over alot.

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