1997 GMC Sonoma Owner's Manual - Page 243

Filling Your Tank [ I The fuel cap is ~ ~ behind a hinged door on the driver's side of your vehicle. While refueling, hang the cap by the tether from the hook on the filler door. To take off the cap, turn it slowly to the left (counterclockwise). The cap has a spring in it; if you let go of the cap too soon, it will spring back to the right. Gasoline vapor is highly flammable. It burns violently, and that can cause very bad injuries. Don't smoke if you're near gasoline refueling or your vehicle. Keep sparks, flames and smoking materials away from gasoline.