someone fwd this msg to me.. to share with everyone 
Pumping gas.... good things to know.
I've been in the petroleum pipeline business for about 31 years,
currently working for the Kinder-Morgan Pipeline here in San Jose,
CA. We deliver about 4 million gallons in a 24-hour period from the
pipe line; one day it's diesel, the next day it's jet fuel and
gasoline. We have 34 storage tanks here with a total capacity of
16,800,000 gallons. Here are some tricks to help you get your
money's worth:
1. Fill up your car or truck in the morning when the temperature is
still cool. Remember that all service stations have their storage
tanks buried
below ground; and the colder the ground, the denser the gasoline.
When it gets warmer gasoline expands, so if you're filling up in
the afternoon or in the evening, what should be a gallon is not
exactly a gallon. In the petroleum business, the specific gravity
and temperature of the fuel (gasoline, diesel, jet fuel, ethanol
and other petroleum products) are significant. Every truckload that
we load is temperature-compensated so that the indicated gallon
gauge is actually the amount pumped. A one-degree rise in
temperature is a big deal for businesses, but service stations
don't have temperature compensation at their pumps.
2. If a tanker truck is filling the station's tank at the time you
want to buy gas, do not fill up; most likely dirt and sludge in the
tank is being stirred up when gas is being delivered, and you might
be transferring that dirt from the bottom of their tank into your
car's tank.
3. Fill up when your gas tank is half-full (or half-empty),
because the more gas you have in your tank the less air there is
and gasoline evaporates rapidly, especially when it's warm
(gasoline storage tanks have an internal floating 'roof' membrane
to act as a barrier between the gas and the atmosphere, thereby
minimizing evaporation).
4. If you look at the trigger you'll see that it has three delivery
settings: slow, medium and high. When you're filling up do not
squeeze the trigger of the nozzle to the high setting. You should
be pumping at the slow setting, thereby minimizing vapors created
while you are pumping. Hoses at the pump are corrugated; the
corrugations act as a return path for vapor recovery from gas that
already has been metered. If you are pumping at the high setting,
the agitated gasoline contains more vapor, which is being sucked
back into the underground tank, so you're getting less gas for your
money. Hope this will help ease your 'pain at the pump'
