GMC Sierra Classic 2007 Owner's Manual page 471

The tethered fuel cap is located behind a hinged
fuel door on the driver's side of the vehicle. If
the vehicle has E85 fuel capability, a yellow cap
with the words "E85 or gasoline" can be seen.
To remove the fuel cap, turn it slowly
counterclockwise. It will require more effort to turn
the fuel cap on the last turn as you loosen it.
CAUTION:
{
Fuel can spray out on you if you open the
fuel cap too quickly. If you spill fuel and
then something ignites it, you could be
badly burned. 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.
If your vehicle is a dual fuel tank chassis cab
model, and it runs out of fuel, refuel the front fuel
tank first to ensure a quick restart.
Be careful not to spill fuel. Do not top off or overfill
the tank and wait a few seconds after you have
finished pumping before removing the nozzle.
Clean fuel from painted surfaces as soon
as possible. See Washing Your Vehicle on
page 588.
471