Buick 2004 Park Avenue Owner's Manual page 252

While refueling, hang the tethered fuel cap from the
hook on the fuel door.
To remove the fuel cap, turn it slowly to the left
(counterclockwise). The fuel cap has a spring in it;
if you let the cap go too soon, it will spring back to
the right.
5-8
CAUTION:
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If you spill fuel and then something ignites it,
you could be badly burned. Fuel can spray out
on you if you open the fuel cap too quickly.
This spray can happen if your tank is nearly full,
and is more likely in hot weather. Open the fuel
cap slowly and wait for any "hiss" noise to stop.
Then unscrew the cap all the way.
Be careful not to spill fuel. Don't top off or overfill your
tank and wait a few seconds after you've finished
pumping before you remove the nozzle. Clean fuel from
painted surfaces as soon as possible. See Cleaning
the Outside of Your Vehicle on page 5-93.