I saw this article in a local paper and thought I would pass the info along to anyone who's interested.
1. Only buy or fill up your car/truck in the early morning when the ground temperature is still cold. All service stations have their storage tanks buried under 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 one degree rise in temperature is a big deal for this business. But the service stations do not have temperature compensation at the pumps.
2. When you're filling up do not squeeze the trigger of the nozzle to a fast mode. Choose slow mode thereby minimizing the vapors that are created while you are pumping. All hose pumps have a vapor return. If you are pumping on the fast rate, some other liquid that goes into your tank becomes vapor. Those vapors are being sucked up and back into the underground storage tank so you're getting less worth for your money.
3. Fill up when your tank is half full (or half empty, depending on how you look at things). The more gas you have in your tank the less air occupying its empty space. Gasoline evaporates faster than you can imagine. Gasoline storage tanks have an internal floating roof. This roof serves as zero clearance between the gas and the atmosphere, so it minimizes the evaporation.
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 gas is being stirred up by the gas being delivered, and you might pick up some of the dirt that normally settles on the bottom.
Hope you find these tips helpful.