I just bought a 2007 Mini Cooper base model. The following is direct from the manual regarding fuel. What appears to be a requirement at first, really turns out to be a recommendation. Someday when the “honeymoon’s” over, I may experiment with regular to see if I notice a difference. The car’s pretty miserly on gas so, for now, I’ve been using premium and it runs great.
“Required fuel - Super Premium gasoline/AKI 91.
This gasoline is highly recommended. However, you may also use gasoline with less AKI. The minimum AKI Rating is 87. If you use gasoline with this minimum AKI Rating, the engine may produce knocking souunds when starting at high outside temperatures. This has no effect on the engine life. Do not use any gasoline below the specified minimum fuel grade. Otherwise the engine could be damaged.”