To be certain, you should:
* Consult your owner's manual: This is the most reliable source for the location of all fluid reservoirs.
* Look for a diagram: Many online repair manuals or parts diagrams for a 1999 Pontiac Montana will show the power steering reservoir's location. Search online using the year, make, and model.
Looking in the engine bay with the diagram in hand will make the process much quicker and easier.