Octane ratings are most definitely not
the same everywhere. There are two types of octane test, the "Research Octane Number" (RON) and the "Motored Octane Number". In Europe, fuel is sold by RON. In fact, in most of the world, fuel is sold by RON.
Of course, in the USA, things have to be different. Typically the MON number is lower than the RON number by about 4. MON represents high load, high speed driving conditions and the test was developed by the Germans since they have the highest speed road network.
Because the Americans never drive anywhere at high speed (their idea of fast doesn't go beyond 100 mph
) they felt the need to include the MON rating too (sic), despite the fact that for many modern fuels the interval between RON and MON is very consistent. Then they invented a new measure called "Pump Octane Number" which isn't a better test (like the Germans invented) but is just a lame-ass average of RON and MON. So typically when US chaps talk about 89 octane fuel they are referring to what we call 91 RON. Of course, being American, they have no idea that the rest of the world exists and so they have no idea that the scales don't match, so they don't feel the need to mention it. You would be frightened to know how many Americans don't realise that the US dollar isn't used everywhere. You would be even more frightened to know that one of them is president.
Unusually for Americans, the number comes out smaller than the rest-of-the-world equivalent. This can be explained by the American oil companies wanting to confuse people from Iowa into buying more expensive fuel than they need for their push-rod iron-head 2-valve motors.
For a less cynical and more factual run-down (in significantly more detail) go to: http://www.repairfaq.org/filipg/AUTO/F_Gasoline6.html
"Are we skidding? That was a good one, daddy!" (Charlotte, 2 years)
"Did you think we were going to crash then?" (Vicki, 32 years)