* 4.2L V8: This engine used premium unleaded gasoline (typically 91 octane or higher).
* 3.2L V6: This engine also used premium unleaded gasoline.
* 4.0L V8 (S8): This high-performance variant of the A8 used premium unleaded gasoline.
* 6.0L W12: This engine, found in the top-of-the-line A8, also used premium unleaded gasoline.
Important Note: Always consult the owner's manual for the specific fuel recommendations for your 2005 Audi A8 model. The manual will provide the exact octane rating required for your vehicle's engine.