system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why it’s common to have 87-octane gasoline in the US but it’s almost always 95-octane in Europe?
gpt
Mostly because the USA and Europe don't measure octane the same way.

Europe uses RON or the "Research Octane Number" which is measured by running an engine under controlled conditions.

In contrast the US uses the AKI or "Anti-Knock Index" which is an average of the RON and MON, the "Motor Octane Number" which uses a similar test engine to RON, but operates it under different standardized conditions.


Roughly speaking:

87 AKI = 91 RON

91 AKI = 93 RON

93 AKI = 98 RON

100 AKI = 104 RON

104 AKI = 108 RON

A similar kind of misconception occurs when people think that the UK has more fuel efficient vehicles because they get more miles or kilometers per gallon. The truth is that the US gallon is 128 fluid ounces and the UK it is 160 fluid ounces, and the vehicles generally have equivalent fuel economy.