A little poser about buying petrol:

So here in the US, north of Philadelphia near Allentown, I see gasoline prices wildly fluctuating. So I saw gas a few days ago for 3.75 a gallon. So you fill up at that price. Then when the tank was half full or half empty, depending on your POV, I see another station with gas at 3.50 a gallon, 8 percent or so cheaper.

The question is, is there any monitory benefit from filling up at the new lower rate when the tank is half full, which used up half the gas from the more expensive gas station versus just driving out the more expensive gas and filling up then?

Originally posted by sonhouse
So here in the US, north of Philadelphia near Allentown, I see gasoline prices wildly fluctuating. So I saw gas a few days ago for 3.75 a gallon. So you fill up at that price. Then when the tank was half full or half empty, depending on your POV, I see another station with gas at 3.50 a gallon, 8 percent or so cheaper.

The question is, is there any moni ...[text shortened]... e more expensive gas station versus just driving out the more expensive gas and filling up then?

That probably depends on the fuel cost rate when you fill the remaining half tank until the two scenarios contain the same volume.

Originally posted by sonhouse
So here in the US, north of Philadelphia near Allentown, I see gasoline prices wildly fluctuating. So I saw gas a few days ago for 3.75 a gallon. So you fill up at that price. Then when the tank was half full or half empty, depending on your POV, I see another station with gas at 3.50 a gallon, 8 percent or so cheaper.

The question is, is there any moni ...[text shortened]... e more expensive gas station versus just driving out the more expensive gas and filling up then?

The problem has too few conditions.
* If you refill and the price goes up you have won
* if it goes down you lost.
* If it stays for the time you need the half of your tank and goes up then you lose.

I fill up when its necessary or I see an offer I think to be cheap.

Originally posted by Ponderable
The problem has too few conditions.
* If you refill and the price goes up you have won
* if it goes down you lost.
* If it stays for the time you need the half of your tank and goes up then you lose.

I fill up when its necessary or I see an offer I think to be cheap.

Sorry, I was assuming for a short time, at least the time it takes to run out the gas, that those two prices remain the same. Does it make a dif then?

Are you asking if you can save money by driving farther away for cheaper gas?

Originally posted by AThousandYoung
Are you asking if you can save money by driving farther away for cheaper gas?

No, I actually posed that one a few years ago. In that case, the cheaper gas station better be frigging close! If it is more than a few miles away, you lose. In this case prices are stable for a couple of weeks in this poser.

Assuming the gasoline is of equivalent quality, then there is no difference.

If gasoline prices are fluctuating however, I would not count on the price staying the same while you are using your other half tank of fuel. Therefore, I would say fill up at the first opportunity at the lower price.

To properly evaluate this you have to evaluate not just fluctuations in gas prices (which you state is constant) but also the opportunity cost of the money spent early to buy the half a tank of gas.

Assume that you take a week to burn through half a tank of gas (which we will call 7 gallons for just to get a rough estimate.)

7X 3.5 = 24.5$
multiply by risk free rate of return
multiply for length of time annualized.

That is assuming that you are carrying no debt. If you are carrying debt of some sort mortgage, credit card etc. then you have to consider risk of late payments etc or paying 24.5 bucks worth of credit off and holding out for a week to buy gas.


None of this is likely to have any real monetary difference but you should be aware of it should the risk free rate of return dramatically increase.

Originally posted by forkedknight
If gasoline prices are fluctuating however, I would not count on the price staying the same while you are using your other half tank of fuel. Therefore, I would say fill up at the first opportunity at the lower price.

This expresses an upward bias to the price of gas, given the current economic woes, I would leave my tank half empty, especially if I could make it through Lbor Day weekend which would mark the end of the summer driving season.

A truly astute (and bored) person might study the crack spread for refiners to come to a better guess and where gasoline might be in the near future.

Always buy your petrol at the cheaper garage signalling your disgust at higher prices.* If no-one bought gas at the higher price the closer garage would reduce its prices.

* It the cheaper garage is BP (Blatant Polluters) boycott it on moral grounds.