learned a few things about mine on trip this weekend
 

now i know this is gonna fire up some self proclaimed chemist and typical know it all guru's :stickpokebut my kid put gas in this weekend and put in the cheap stuff. i could tell absolutely zero difference in how it ran which came as a complete surprise, next was that there wasnt a noticable power difference and last but not least it actually got better fuel mileage! and this is an exact comparison because i made the exact same trip last weekend and i always use exxon 93. and at 30 to 50 cents per gallon difference :nanana::rofl:

Not news...do Search Tab look up: pages of threads on the topic of
"which gas", etc.

A poster named JCL and others, have good views/opins on less than
93/91 octane.
GL, mD

Not much of a surprise. You will likely benefit from the higher AKI more in the heat of summer than now. Any measurable mileage difference is more likely to be due to differences in ethanol % than in fuel (the fuels have the same calorific value, apart from the ethanol added in, which has much less energy when burned).

My best fuel mileage ever in my X5 3.0 was on 89, and I measured it a lot, tank fill to tank fill (using the OBC only as a validation).

If the engine sensed knock, and retarded the timing to protect itself, you would likely notice a power difference, but only at those moments when the timing was being retarded, which would be a small percentage of the time you are driving it. I would have thought that the twin turbo in your car would be more able to take advantage of the higher AKI, but there has been so much advancement in combustion chamber design, that the old rules about what AKI is required for a specific compression ratio have pretty much become irrelevant.

My 535 (twin turbo six) does feel stronger on higher AKI, but I haven't seen any mileage difference from the few times I have checked it, so I stopped measuring.

Wow...you buy a car for 80-90k but care about fuel consumption. *LOL*
In Germany, we pay two to three times the prices you pay in the US and I still don't care (not that it doesn't bother me) as long as my car provides the maximum performance and reliability.

Of course the higher octane fuel shows it's potential mostly in the higher speed range but I would really have a bad feeling of using lower octane gas on such a car, especially since "behind the curtains", the knock sensor takes care of the stuff. To each his own I guess...

Btw: most people with high performance turbo charged engines over here in Germany are using 100 octane (which would translate to 97 octane in the US) gas which costs aprox. 1.65 EUR a liter. This would be aprox. 8 USD a gallon. Cheers. :D

Your 100 RON is pretty close to 94 AKI, which we have at the pump here. My 535i runs nicely on it.

Some day we will move past the stage where fuel efficiency is all about cost. Can't it also be about more efficient use of our resources? My company gas card paid for all my fuel purchases in my personal car but I still measured the mileage.