The following is adapted from a post on facebook by Mark Diffie. Since the author indicated this should be shared, I thought I would do so here because the information is reasonably useful.
Here are some tips to get more of your money's worth for every gallon of gasoline you pump.
TIP 1: Only fill up your car or truck in the early morning when the ground temperature is still cold. All service stations have their storage tanks buried below ground. The colder the ground the more dense the gasoline. When it gets warmer gasoline expands, so buying in the afternoon or in the evening your gallon is not exactly a gallon.
In the petroleum business, the specific gravity and the temperature of the gasoline, diesel and jet fuel, ethanol and other petroleum products plays an important role. A 1-degree rise in temperature is a big deal. That's why these variables are controlled. But service stations do not have temperature compensation at the pumps. Even the trucks that transport fuel are temperature compensated so that every gallon is actually the exact amount.
TIP 2: When you're filling your vehicle do not squeeze the trigger of the nozzle to its fastest mode. If you look, you will see that the trigger has three (3) stages: low, medium, and high. The slower you pump, the more you minimize the vapors created. If you are pumping at the fastest rate, some of the liquid that goes to your tank will immediately vaporize. Thus, you're getting less gas for your money.
TIP 3: This is one of the most important tips: fill up when your gas tank is HALF FULL or HALF EMPTY. The reason for this is the more gas you have in your tank the less air occupying its empty space. Gasoline evaporates faster than you can imagine. Refinery storage tanks have an internal floating roof. This roof serves as zero clearance between the gas and the atmosphere, so it minimizes the evaporation. Your vehicle, however, does not have this.
(If you ever wondered why the needle seems to move faster toward "E" the further away it is from "F," the above tip might explain this. - ed.)
TIP 4: If there is a gasoline truck pumping into the storage tanks when you stop to buy gas, DO NOT fill up--most likely the gasoline is being stirred up as the gas is being delivered, and you might pick up some of the dirt that normally settles on the bottom of the service station's storage tank.
Hope this will help you get the most value for your money. DO SHARE THESE TIPS WITH OTHERS!