GMC 2004 Sonoma Owner's Manual page 252

While refueling, hang the cap by the tether from the
hook on the fuel filler door.
To remove the fuel cap, turn it slowly to the left
(counterclockwise).
5-8
CAUTION:
{
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.
CAUTION:
{
If a fire starts while you are refueling, do not
remove the nozzle. Shut off the flow of fuel by
shutting off the pump or by notifying the
station attendant. Leave the area immediately.