The perfect pump. It seldom happens, but it is when the automatic shutoff on the gas pump clicks at an exact even dollar amount. It is even more special if it’s on a big dollar amount, like $20 instead of $17. For those obsessed with having a round number when pumping gas, they can be ridiculed by their friends and spouses. A recent survey has determined that having a round number on a fill up is something many people are intent on doing. Let us take a look at the numbers, and then discuss why overpumping to get a round number is not necessarily a good thing.

gas pump

When we fill gasoline we like seeing even numbers. (Photo: Shutterstock)

The Journal of Economic Psychology pulled refueling information from over 1,000 customers at a gas station in New York, and discovered that 60% of all transactions with the cents being zero (Example: $7.00). An additional 7% ended in a penny (Example: $7.01), which could indicate that the person filling up intended on having a full dollar amount, but the pump pumped a little bit extra into the tank. The odds of randomly hitting zero cents on a fill up is only 1%, showing that we are indeed looking for a perfect pump.

The same applies to whole dollar amounts as well. Over 50% of the transactions ended in 0 or 5 (Example: $5 or $10), even though the likelihood of hitting one of those randomly is only 20%. Perhaps it is easier for people to balance their checkbooks when the dollar amounts are whole dollars, but with many people using credit cards it is surprising that that trend still exists.


Accepting an odd number and not overfilling can save costly repairs to a vehicle. (Photo: Shutterstock)

Overfilling a gas tank beyond the automatic shutoff is not a good idea. At the very least, there is a risk of the fuel spilling out of the gas tank which would be wasteful. That overflowing fuel can leak onto the vehicle and damage the paint, or can spray back and damage your clothing. A worse situation would be fuel getting into the evaporator system in the tank, causing damage to the emission controls of the vehicle. That could end up being a costly repair. When refilling a gas tank, we strongly recommend stopping the refueling process when the automatic shutoff clicks to the off position, regardless of dollar amount shown on the display.

Human brains work in unique ways, and we do have a fascination with numbers. While we hope for even dollar amount fill ups at the gas station, gasoline is priced to 9/10ths of one cent when it’s distributed. But for those that think its weird to round fill ups to a round cent, there is now proof to show it is more common than not.