GMC Yukon Denali 2003 Owner's Manual page 306

While refueling, hang the fuel cap by the tether using
the hook located on the inside of the filler door.
To remove the fuel cap, turn it slowly to the left
(counterclockwise).
5-8
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CAUTION:
If you get fuel on yourself 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. Clean fuel from painted
surfaces as soon as possible. See Cleaning the Outside
of Your Vehicle on page 5-87 .