US & Canadian Octane Numbers

Here's what I found out. It may not be what everyone expected. But if, as I originally said, It's listed as (R+M)/2 on the pump its all the same standard.

Measurement methods
The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.
There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.
In most countries (including all of Europe and Australia) the "headline" octane rating, shown on the pump, is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, the octane shown in the United States is 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, is 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and some even deliver 98 (RON) or 100 (RON).
It is possible for a fuel to have a RON greater than 100, because iso-octane is not the most knock-resistant substance available. Racing fuels, AvGas, LPG, and alcohol fuels such as methanol or ethanol can have octane ratings of 110 or significantly higher - ethanol's RON is 129 (MON 102, AKI 116). Typical "octane booster" gasoline additives include tetra-ethyl lead, MTBE and toluene. Tetra-ethyl lead (the additive used in leaded gasoline) is easily decomposed to its component radicals, which react with the radicals from the fuel and oxygen that start the combustion, thereby delaying ignition, leading to an increased octane number.

From Shell North America:
Firstly, keep in mind that a gasoline’s octane rating is simply a measurement of the fuel’s ability to resist engine knocking. It does not refer to a substance or to the quantity of energy or power in the fuel. More correctly, an octane rating is often called an “anti-knock index”.
When unburned gasoline vapours spontaneously explode in the cylinder before the expanding flame in the combustion cylinder reaches them, it actually causes two simultaneous explosions (the other is from the spark plug). This results in a knocking or pinging sound, and when an engine knocks the result is a reduction in the power it delivers.
The higher a fuel's octane number, the higher its resistance to engine knock.
Technically there are three different "octane numbers" associated with every gasoline.
1 The Research Octane Number, or RON, is measured under fairly easy test conditions.
2-The Motor Octane Number, or MON, is a tougher test measured at higher engine speed and temperature.
3-The value that relates most closely to actual driving conditions is the average of these two values: Road Octane Number = (RON + MON)/2 or (R+M)/2. This Road Octane value is the one referred to in Shell stations: Shell Bronze gasoline has an octane rating of 87, Shell Silver is 89 and Shell V-Power is 91.
Occasionally, less scrupulous Canadian gasoline outlets will use the confusion of these different octane measurements to exaggerate their octane rating claims, by advertising their fuel's Research Octane Number - which will be higher than the Road Octane Number. It is also a common practice in many European countries to advertise the Research Octane Number on their pumps, so you may see unexpectedly high octane values when travelling abroad. In Canada, motorists should always be sure that the octane number a vendor advertises is its Road Octane value, not its RON.
However, there are some exceptions to this, and it must be noted that if the owner’s manual specifies using gasoline with an octane rating of 89 or 91, then that’s what you should use because that’s what the engine is designed and tuned for.
One - and a very important - exception is that when a vehicle gets older, the normal build-up of fuel- and lubricant-related deposits in the engine can increase the fuel octane number a car requires to prevent engine knock. For this reason, if a car more than a couple of years old experiences engine knocking, the problem may be solved simply by moving to the gasoline with the next-higher anti-knock index.
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