In the US (and probably Canada as well), it is possible to pay at a gas station either with a credit card often with a fee (in the US) or cash. If I pay cash, gas stations often require to prepay for the gas.

However, I always wonder how much I should prepay. I suppose that people owning a car know how much filling the tank is worth. But I do not own a car and sometimes rent a car to visit the US, and each car has different fuel consumption. I usually estimate how much 100km is worth in terms of fuel and prepay close to the estimated amount and it just works.

But what is the expected behaviour? Am I supposed not to fill my tank entirely every time? Can I prepay a large amount and ask for the difference between what I prepaid and what I filled? Could I pay a way larger amount when i don't know (when the oil price is low, prepaying 40 or 60 USD might be seen as way too much). This question might sound a bit weird or obvious to some, but every time I rent a car I am wondering what the etiquette is.

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    If you prepay and it turns out you prepaid way too much, you might feel a bit silly, but no harm is done and you're not being rude. It isn't really any more work for the cashier to give you $38.40 in change than $1.37. Commented Feb 20, 2015 at 4:12
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    Don't feel silly, I never know the answer to this question when I find a station like this (e.g. doesn't take credit cards and have to prepay).
    – user23030
    Commented Feb 20, 2015 at 15:25
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    This is so strange, in europe you pay after you fill the tank so you know how much to pay! Commented Feb 20, 2015 at 15:43
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    @AndreasBonini It used to be like that in the United States as well but I guess too many people would fill up their tank, then just drive away and not pay. So now most places in the US make you pay first. I just use my bank debit card and there are no fees.
    – Kenny
    Commented Feb 20, 2015 at 16:14
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    @ChrisH: I have used a Canadian Visa card at many gas stations in many states in the US. All you have to do when required to enter the zip code, is to use the three numbers from your postal code, followed by two zeroes. Commented Feb 21, 2015 at 4:19

9 Answers 9


So, you should prepay for however much gas you intend to buy. In most cases, you'll probably want to either fill the gas tank, or just buy an amount of gas that corresponds to a nice round dollar amount like 20 dollars, to make the transaction quick and easy.

If you want to top off the tank, just prepay for an amount that you know exceeds the amount required to fill it, and then request change after the tank is topped off.

As to determining the amount required to fill the tank, well, you can generally guesstimate that with a fair degree of confidence just by looking at the gas gauge in your car. If it's at the halfway mark, you have room for half a tank of gas. The vast majority of cars in the US have gas tanks with a capacity between 12 and 20 gallons. (You'll see still higher capacities on trucks and SUV's). While you can get the exact number by checking the owners manual (on a rental, this can usually be found in the glove compartment), you can also figure this out pretty quickly the first time you fill up the car when it's low on gas. After that, it's a simple matter of multiplication of the gas price, times your (rough estimate) of the number of empty gallons you need filled. It's helpful to overestimate in this case, as, again, you can easily ask for change.

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    the size of your gas tank depends heavily on what kind of car you have; 12-15 gallons is right for compact cars, but sedans often have ~20 and SUVs ~30.
    – KutuluMike
    Commented Feb 20, 2015 at 13:32
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    Whoa, tanks are that big? My Honda Accord holds ~17 gallons and it feels huge. My wife's Hyundai Accent is ~11 gallons. Commented Feb 20, 2015 at 17:36
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    @MooingDuck Ford Bronco is the first example I can think of. My uncle's Bronco had 2 11-gallon tanks and a 13-gallon tank, but that 3rd tank wasn't stock. Others I've seen have tanks ranging up to 33 gallons based on a quick Google search.
    – BlueBuddy
    Commented Feb 20, 2015 at 17:41
  • Until I bought my Scion, every car (SUV) I'd owned had a 20+ gallon tank Commented Feb 20, 2015 at 21:59
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    In my experience, actually, when the gas gauge is at the halfway mark, you've got closer to 1/3 of a tank left, not 1/2.
    – user438
    Commented Feb 22, 2015 at 17:00

Why not use a credit card and ask for a full tank? That's what I do.

If you want to pre-pay in cash, it's ok to pay more than you need and get the change back. Cars usually have gas tanks that are 10-20 gallons in size. So if it is half full, estimate 10 gallons and pay for 10 x $currentpriceingallons. So if it is $3 per gallon, prepay $30 (or $40 to be safe).

Note that if you pay too little, all that will happen is that the pump will shut off. At that point, you can either hang up the pump and drive away (no need to return to the attendant unless you need a receipt). Or you can go back inside and give a little more money to the attendant to top it off. I usually just hang up the pump and drive off. Much easier and simpler.

Note that if you are topping off the tank before returning it to the rental car agency, they may ask you for a receipt in order to prove that the tank is full. So that would be a reason to either use a credit card and get a receipt at the pump, or to head back inside and ask for a receipt.

  • 10 - 11 gallon tanks are fairly common on small cars, such as the old Volkswagen Beetle, and new small cars like the Toyota Yaris, Smart ForTwo, and Fiat 500. The Chevy Volt has a 9 gallon tank. cararac.com/fuel_tank_size
    – Jasper
    Commented Feb 20, 2015 at 20:56
  • Many gas stations offer cheaper prices if you pay in cash than if you pay with credit card.
    – user102008
    Commented Feb 21, 2015 at 0:39
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    Only around 2-5c cheaper, which turns out to be around 50 cents or less. If it saves me 5 minutes waiting in line behind eight people buying lottery tickets and cigarettes, it's worth it.
    – RoboKaren
    Commented Feb 21, 2015 at 5:19
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    @Andy, here in central California cash discounts for gas are fairly common.
    – Joe
    Commented Feb 21, 2015 at 17:42
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    Also, regarding the credit card, a simple explanation is the fee for using it. I do not have an American card and my bank charges no fee for some withdrawal but 1+ dollar on every payment. So I'd rather avoid 1+ dollar on every 15-20 spent.
    – Vince
    Commented Feb 23, 2015 at 22:06

You should pay enough cash to cover for the quantity of fuel you want to buy. In case you prepaid more than needed you should have no problem getting your change back from the cashier. On the other hand should you have prepaid less than needed, when refueling the machine should cut you off as soon as the prepaid amount is reached. You can always prepay a bit more and begin refueling again. Once again, no harm done there.


Americans used to be able to pay after filling the fuel tank, but too many people just drove away without paying (they stole from the gas station).

Most MAJOR brand gas stations (Exxon, Mobil, Sunoco, Shell, Texaco) do NOT charge more to use a credit card, but you need to check before using your credit card. Usually the sign will say "Cash" under the price if there is a discount for using Cash. Sometimes the sign will say "Cash or Credit" which means it is the same price.

If you want to pay cash, you guess how much you need, pay in advance, and then collect your change. There is no shame in getting back the extra money you gave the attendant. If you don't get your money back, the person in the booth will just take the extra money out of the drawer and keep it themselves.

The good news is that fuel is MUCH cheaper here than it is in most of Europe. Here, gas is cheap and beer is expensive. In Europe, beer is cheap and gas is expensive. :-)


AFAIK in the US it is illegal to charge a different price for gas depending on payment method. So the only fees you will incur in paying by credit card is whatever the issuing bank tacks on to the current exchange rate - which is often a better rate than you get exchanging cash for USD in the first place. So just pump a full tank and pay by credit card, and be done with it. :) Apparently, as pointed out in the comments, in a very unfortunate turn of events this is no longer true. What I can still say though is depending on the difference in price and difference in exchange rate from your home currency, is that paying by credit card may indeed still be the better rate. In general, you often get a much better exchange rate when you pay with your credit card as compared to exchanging cash for USD then using this.

Gas stations do sometimes offer prepaid cards which might give you a discount though. Like you might be able to get a $50 card for slightly less than $50. If you can get one and know you'll use that much gas, go for it. But for short stays, it's most likely not worth the hassle and prepaid cards are often not refundable.

If, however, by "prepay" you actually mean "give the attendant cash up front before you pump your gas", just give them something reasonable based on how much you want to fill up. If you want to just put $10 in, do that. Otherwise give them a bank note or two ($20? $40? $50?), pump the gas, and go back for the change. Honestly, the only time you'll get a dirty look is if you give them $43.27 upfront, pump $21.36, then expect them to give you change back.

It's also worth noting in the US most gas stations will refuse a $100 bill, and even $50s are a gamble depending on the part of town. It's best to stick to denominations of $20 or lower.

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    The legality of different prices for different payment methods depends on which state you are in. In Massachusetts, for example, it IS legal (and common) to charge a substantially lower cash-only price. Commented Feb 20, 2015 at 12:06
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    @NicolasHolthaus: Same in Colorado, though often the cash price is also available if you use a debit card with a PIN transaction (lower merchant fees). So far it seems that it's mostly gas stations at grocery stores that have different cash and credit prices; the ubiquitous name-brand corner gas stations don't seem to be going this route yet. Commented Feb 20, 2015 at 15:30
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    @BrianDHall Since the massive settlement against Visa and Mastercard a couple of years ago, merchants are free again to surcharge, except where prohibited by law.
    – choster
    Commented Feb 20, 2015 at 16:43
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    @choster Thanks for that link, I was utterly unaware that happened! I retract my comment :)
    – BrianH
    Commented Feb 20, 2015 at 16:56
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    It is legal and practiced at most cheap gas stations in California.
    – user102008
    Commented Feb 21, 2015 at 0:40

My simple answer is: estimate. I also offer here a more in-depth explanation in case you wonder why a gas station would put their customer through such an experience.

I imagine that the reason you've struggled with this is that the system isn't exactly optimized for your particular usage scenario.

Many people use credit cards or debit cards, which allows the equipment at the gas station to simply verify that the card is in good enough of standing (e.g., not reported as stolen), then remember the number, and then actually charge the exact right amount. Gas stations probably get a lot more people paying amounts like $20.82 or $23.16, compared to the days when more people paid cash and would try to pay $20.00 even (or $20.01, and spend a coin they find in a pocket or ash tray or something). People who paid cash would often try to hit an even dollar amount; customers with cards probably pay more on average. Especially since the next gas payment may be to a competing gas station, they want to get the money now. Supporting the use of a payment (credit or debit) card is a system that works perfectly well for very many customers these days.

Out of the people who do still pay cash, many of them probably just pay $20 or $40 or whatever, depending on the price of gas, and then they don't fill the car up. Then the car isn't absolutely filled up, but that's okay; they'll just go to another gas station a bit sooner and pay more cash there, then. So the system (of requiring pre-payment) is working out decently well for these customers as well.

As a traveler who rents a car, you have a somewhat unique need to fill the car up, because you don't want to get charged a fee for returning a car that isn't filled up.

Many of the gas station customers are not travelers. But even among travelers, you may be unique. Actually, many travelers probably use cards; even if they do carry cash also, it is because they want to keep that cash for emergency situations, and so they don't want to just dump all the cash on a purchase like gasoline. So they will use the card for that.

Out of the travelers who do prefer to pay cash for things, some of them probably just said "yes" when the clerk at the car rental asked if they want to purchase "gas protection" or whatever they call it, where instead of a super high fee for returning an empty tank, they charge a flat rate which is based on a medium-rate fee per gallon, multiplied by the number of gallons of an empty tank. So the only people in your position are the people who want to pay the lower rate of normal gas station prices, but who want to pay cash, and who are near the end of their trip (so they are trying to precisely estimate how much it will cost).

So after taking care of non-travelers who use cards, non-travelers who pay with cash, travelers who pay with cards, and travelers who don't need to precisely estimate how much will fill up a tank, we're left to people in your position. Surely this position does not represent the majority of gasoline purchases. Some gas stations might also only require pre-payment for cash after a certain time of the day (like 5pm or 7pm), further narrowing down who this even affects.

For people in your position, the "expected behavior" (which was asked about) is to simply estimate. Yes, that may mean doing a bit of math, which might be a bit more of a struggle than what most companies want to put their customers through. But, remember, you're not representing the average common case that they made the regulations around. The regulations aren't really designed around people in your situation. The regulations to demand pre-payment are probably mostly designed to reduce situations of non-payment. Maybe too many cash payers will go to McDonald's, then forget that they did, and later fill their tank without remembering that they now have less money than they expected.

What are the gas stations expecting? They expect that the system in place works well enough for most people, and that people in less common situations will simply tolerate the idiosyncrasies/inconveniences imposed by the system. That is the typical "etiquette" that you were asking about. So, to be specific for this particular scenario, what people generally expect a person would do in your situation is to perform a bit of estimating. And, if your estimation is a bit off, then you'll somehow live with the consequences.

I hope that mostly answers the main question. Since you threw in a few specific questions, here are a few specific matching answers.

Am I supposed not to fill my tank entirely every time?

I'm sure that the owners of a gas station are happy to maximize income by having you fill a tank. If that means you pre-pay $30, then find out that wasn't enough, and you walk to the cash register to pay a bit more, then that's fine.

Can I prepay a large amount and ask for the difference between what I prepaid and what I filled? Could I pay a way larger amount when i don't know

Usually, yes, but that might not be guaranteed to work in all cases. There may be some limitations, particularly if the cash register doesn't have much money to be giving a certain amount of change. You can simply ask the cashier. For instance, many cashiers get unhappy when someone springs a $100 bill on them. But if you ask ahead of time, they usually aren't offended. Just ask if you can pay $50, but mention you don't know just how thirsty your car's gas tank is, and you might need up to $35 of it back. Ask, "Is that okay?" If they say yes, you ought to be fine.

I part this analysis with the following idea. If you pay for more gasoline than what you pump, and then you're too embarrassed to want to walk all the way back over to the cash register just to get your $1.37, another option may be to walk back to the cash register with an unpurchased snack in hand. Then, instead of the cashier just giving away money that's in the till, at least the cashier will feel like (s)he is completing another purchase, which is good for the company. Additional bonuses for you may include deliciousness (yay!) and obesity (hmmm... grrr).


While the general answer is "enough to cover the fuel you'll pump" beware that it's not exactly unusual if it's late or otherwise high risk for the station to have little in the way of cash readily available. The money is stored in a machine that limits the rate at which it's dispensed. If you use a $100 bill to buy $20 bucks worth of gas you might have a bit of a wait for your change.

An example of such a safe:


  • Have any photos or links about these machines? Sounds like a mini-ATM, and not nearly as useful or cheap as a sturdy safe the employees drop extra cash in (just keeping $100 or so for the float/change)
    – Xen2050
    Commented Feb 21, 2015 at 8:22
  • @Xen2050 Time-delay safes are quite common. Commented Feb 21, 2015 at 19:05
  • @MichaelHampton These aren't typical time-delay safes. Rather, they are safes with rate-limited dispensers. You push a button for what sort of money you want out, it gives it to you--but then waits a while before it gives you more. The idea is to make it impractical for an armed robber to get much--the clerk is NOT able to speed it up. Commented Feb 22, 2015 at 0:00

Why are you asking how much cash you should be paying for gas? That is up to you. First know your car: how many gallons does it hold? Then look at your gas gauge. Are you down to half? Okay, if your tank is 20 gallons total, say you need 10 gallons. But gauges aren't always accurate. Make that number 12 or 13 gallons. Then, look at the big sign of gas prices as you enter the lot. Then pay for what that would be and just come back for the little change.

It is also much easier if you just stick your card in at the pump and start pumping, it'll shut off all on its own when its full. No need to ever know "how much it needs", the computer and sensor do the work for you.

Also, never buy items in the gas station and then tell the clerk you want the rest of your money for gas, the clerk has to enter in a number as soon as they are prompted that you are getting gas. They are waiting to hear you tell them a number, not a math problem which their computers don't have a function to take on. Their computers can only figure out the amount of change you get back.

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    I think, there is an answer hidden in here. However, it may need editing to be more visible and potentially toning down the tone a little.
    – Jan
    Commented Sep 17, 2016 at 10:38
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    @Mark no need to be that negative. Your questions are answered in my question. What's obvious to you isn't for me, and vice versa. Plus, your answer has pretty much the same content as most of the other answers. If it was just to be rude, you could have kept it to yourself.
    – Vince
    Commented Sep 17, 2016 at 10:55

The issue over using a debit or credit card is that if you are a traveler from Europe or Australia, the blessed gas pump asks for your non-existent zipcode. We have postcodes with alphanumerics. Apparently some Canadian cards have been accepted by using the numbers bits of the postal code and right filling with zeroes. It is all very much hit or miss. I reckon the gas company gift cards might be a solution if you buy one where you know there are plenty of their filling stations on your route.


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