There are 2 widely used rating systems used in the world of fuel.  Around the world the most common is RON (Research Octane Number), which is found by utilizing a knock engine.  Here in the US we use AKI (Anti-Knock Index), while AKI is determined by taking the average of MON (Motor Octane Number) and RON.  While the fuels are technically the same, the numbers at the pumps will differ. For example, 93 octane AKI, here in the US, is found by taking 88 octane MON added to 98 octane RON (used around the world) and dividing by 2.  

93 AKI = (88+98)/2