To be certain, you should:
* Consult your owner's manual: This is the best resource for the precise location.
* Use a repair manual specific to your 1997 Buick LeSabre: A Haynes or Chilton manual will have diagrams and detailed information.
* Look at online images: Search for "1997 Buick LeSabre oil pressure sending unit location" on Google Images. Comparing images to your engine should help you locate it.
Remember to be careful when working around hot engine parts. Allow the engine to cool completely before attempting any repairs or inspections.