Here is part of an email I received from someone I know about this same subject.

This is a true story, so read it carefully. On April 24,
2008, I stopped at a Kangaroo

BP gas station, located at 1325 Main Street, Cartersville,
GA. My truck's gas gauge was on 1/4 of a tank. I use the
mid-grade, which was priced at $3.71 per gallon. When my tank is at this
point, it takes somewhere around 14 gallon's to fill it up. When the pump
showed 14 gallons had been pumped I began to slow it down, then to my surprise
it went to 15, then 16. I even looked under my truck to see if it was
being spilled. It was not. Then it showed 17 gallons had been
pumped. It stopped at almost 18 gallons. This was very strange to
me, since my truck has only an 18 gallon tank. I went on my way a little
confused, then on the evening news I heard a report that 1 out of 4 gas stations
had calibrated their pumps to show more gas had been pumped than a person
actually got.



Here is how to check a pump to see if you are getting the right
amount:

Whichever grade you are using, put EXACTLY 10 GALLONS in your
tank, then look at the dollar amount, if the dollar amount is
not EXACTLY 10 times the price of the fuel you have chosen,
then the pumps are rigged. In my case as I said the mid-grade was $3.71
9/10 per gallon, my dollar amount for 10 gallons should have been $37.19.
If I had only check the pump. It doesn't matter where you pump gas, please
check the 10 gallon price. If you do find a station that is cheating,
contact the Georgia Agriculture Department, and direct your comments to Tommy
Irvin, Commissioner. In other states contact proper
authorities.