In North Ameria we use the octane rating PON (Pump Octane Number), European and most other countries use RON (Research Octane Number). Basically 95 RON = 91 PON.... so to answer your question use 95 as Audi recommends.

...... now close this mess of a thread.

 

You should use whatever the car is tuned for (which it should say on the gas door), any higher octane rating than what the car is desighned to run causes the car to run rich which will prematurely ruin o2 sensors, clogg up catylitic converters, and could possibly burn up exhaust valves depending on length of time and how rich it is running. Also useing a higher octane fuel than the tune is set for will decrease performance and decrease gas mileage contrary to what some people think.