We use different ways of calculating octane (copied this from the interweb):
"It turns out that in Europe, the octane number posted is determined by the RON method (if you live in Europe, check the small print on the gas pump next time you fill 'er up. Wait, filling it up requires taking out a loan nowadays...). In the USA, the number posted is according to the "(R+M)/2" method. Turns out that this is simply the average of the RON number and the MON number. So, would the MON number typically be lower than the RON number? The answer is....yes! Apparently, for modern fuels, the difference between RON and MON (also called sensitivity) is about 10 (RON is higher than MON). Knowing this, we can now calculate the following:
87 octane in the USA = 92 octane in Europe
89 octane in the USA= 94 octane in Europe
92 octane in the USA = 97 octane in Europe
Go figure, huh? It seems these regular and premium fuels have roughly the same octane rating after all."
Gulf Coast, is this correct?