Definition:
Octane rating is a fuel's ability to resist detonation and is classified by three main rating types:
All tests use blends of iso-octane and heptane as the reference fuels.
RON (Research Octane Number) is determined by burning fuel in a test engine running under mild and low load conditions, and comparing the results to the reference fuels.
MON (Motor Octane Number) is determined by burning fuel in a test engine running under severe and sustained high load, high speed conditions, and comparing the results to the reference fuels.
(R+M)/2 (Pump Octane Number) as the name implies, is determined by adding together a fuel's RON and MON ratings and dividing by two. This is the common rating found on pumps in North America.
Pronunciation: ok tayn ray ting
Also Known As: Octane Number
Examples: Ethanol has an (R+M)/2 octane rating of 113.