Buick 2001 LeSabre Owner's Manual page 276

The cap is located behind a hinged door on the driver's
side of the vehicle.
6-6
While refueling, hang the tethered cap from the hook 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.