Don't know how it is in the US, but down in Australia, we run minimum 95 octane for Bimmer's. I run 98 octane premium unleaded in my car. I noticed slight better fuel consumption with 98 over 95. When I first got my car I ran 91 octane on 1.5 tank refills and it ran like crap. It wasn't pinging just lacking power more than anything. They have even introduced 100 octane with 5%ethanol blend.
