Buick 1999 Riviera Owner's Manual page 238

6-6
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.
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