1999 Buick Riviera Owner's Manual - Page 238

yellowblue The fuel door can also be opened by using the release in the trunk compartment, on the driver's side of the vehicle. While refueling, hang the tethered cap in the notch on the fuel door. To remove 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. 6-6