Generally, octane ratings are higher in Europe than they are in North America and most other parts of the world. This is especially true when comparing the lowest available octane level in each country. In many parts of Europe, 95 RON (90-91 AKI) is the minimum available standard, with 97/98 RON being higher specification (being called Super Unleaded). The higher rating seen in Europe is an artifact of a different underlying measuring procedure. In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in Canada, the United States 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, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in Canada and the US, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90–91 US AKI=(R+M)/2, and deliver 98, 99 or 100 (RON) (93-94 AKI) labeled as Super Unleaded - thus regular petrol sold in much of Europe corresponds to premium sold in the United States.

in the Rocky Mountain (high altitude) states, 85 AKI is the minimum octane, and 91 AKI is the maximum octane available in fuel. The reason for this is that in higher-altitude areas, a typical naturally-aspirated engine draws in less air mass per cycle due to the reduced density of the atmosphere. This directly translates to less fuel and reduced absolute compression in the cylinder, therefore deterring knock. It is safe to fill up a carbureted car that normally takes 87 AKI fuel at sea level with 85 AKI fuel in the mountains, but at sea level the fuel may cause damage to the engine. A disadvantage to this strategy is that most turbocharged vehicles are unable to produce full power, even when using the "premium" 91 AKI fuel. In some east coast states, up to 94 AKI is available [1]. In parts of the Midwest (primarily Minnesota, Iowa, Illinois and Missouri) ethanol based E-85 fuel with 105 AKI is available [2]. Often, filling stations near US racing tracks will offer higher octane levels such as 100 AKI. California fuel stations will offer 87, 89, and 91 AKI octane fuels, and at some stations, 100 AKI or higher octane, sold as racing fuel. Until summer 2001 before the phase-out of methyl tert-butyl ether aka MTBE as an octane enhancer additive, 92 AKI was offered in lieu of 91.