Octane numbers in the U.S. are of two types, Research Octane Number and Motor Octane Number. The number usually report at the pump is the average of the two, (R+M)/2. The research number is higher than the motor number for a given gasoline.
A misconception is that higher octane is more powerful gas. This is not true. The higher octane means that an engine running it will be less likely to knock. Knocking is an autoignition, similar to the way a diesel engine runs, based on the pressure and temperature in the combustion chamber.
Race cars often have a higher compression ratio, so they require a higher octane gasoline to prevent knocking or pre-ignition.
Many cars in the U.S. today are built with a lower compression engine, for example 8:1 or 8.5:1 compression. For this reason and because the ignition systems have improved, there is better control of when the spark occurs, the engines can run on a lower octane.
I don't which octane numbers are reported in Europe, but it is quite possible that they report the Research numbers on the gas pumps.
Wes R.
