WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Fuel Fill Pipe
Courtesy of GENERAL MOTORS CORP.
The fuel fill pipe (2) has a built-in restrictor and deflector in order to prevent refueling with leaded fuel.