WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. 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 a deflector in order to prevent refueling with leaded fuel.