There was an old discussion about octane EU vs US.
Found by Search.

No matter if the gas engine is a N or M,
the higher octane gives better power.

The reg gas in US is lower octane than in the EU.
All BMW US enigines are given less hp values do to this fact.

Just use the 98 octane, you'll get more out of your E60 engine.

 

There are also differences in HP. The EU generally uses PS horsepower while the US uses the correct SAE. The measure isn't 1:1 so there are some additional differences.

1 PS = 0.98632 hp (SAE)

Also the US measure for fuel octane is about 4-5 points lower than the equivalent measure used in most areas of the EU. Therefore, the common premium fuel in the US is 91 Octane (AKI or (R+M)/2) and the comparable EU equivalent would be about 95-96 Octane (RON). There are a few stations (Shell) here that also offer 93 Octane (AKI) fuel that would be about the same as the EU's 98 Octane (RON).

This should really be made into a sticky since it comes up all the time.

 

Hi fellows!

I found this video called "Which fuel produce more HP" made by Fifth Gear.
It is a simple video with some empirical evidence on this matter.

Here:
http://www.autoclips.net/detail.php?id_video=3264


Best regards
Fkuti

 

bmws here are rated for 98 octane petrol.. so they can vary from 98 to 92

 

The BMW engine sounds too good to be true.