Why can the US make do with lower RON fuels?

**JackFlash** · December 7th, 2012 01:05 AM

On a recent trip to the US, I rented a Dodge Avenger. When I needed to refuel, I checked on the car's manual. To my surprise, the recommended fuel was "regular" with a RON of 87. So off to the gas station I went - Chevron to be exact - and was further surprised to see that "mid-grade" gas was 89 RON while "premium" was at 91-93 RON. Interestingly, RON in the PH is between 93-100.

So here's my question to the motoring experts. How come the US can make do with lower RONs than the PH? I was just thinking that in a developing country like ours, our car manufacturers could have provided engines that tun on lower RON thereby giving us lower priced gas. The conspiracy theorist in me is further convinced that the automotive and petroleum industry is out to suck us motorists dry.

**ronki** · December 7th, 2012 01:09 AM

Right. Kahit sa manual ng local cars natin, mataas na ang 93 octane.

**Alpha_One** · December 7th, 2012 02:03 AM

The answer is quite mundane, actually: The US does not use Research Octane Number (RON) to measure octane rating, but the Anti-Knock Index (AKI). 89 AKI is roughly equivalent to 95 RON. In other words, more or less they get exactly the same fuel that we do.

Measuring octane - RON, MON and the difference between America and the rest of the world.

Just so you know, the octane number is actually an imprecise measure of the maximum compression ratio at which a particular fuel can be burned in an engine without detonation. There are actually two numbers - RON (Research octane number) and MON (Motor Octane Number). The RON simulates fuel performance under low severity engine operation. The MON simulates more severe operation that might be incurred at high speed or high load and can be as much as 10 points lower than the RON. In Europe, what you'll see on the petrol pumps is the RON. However, in America, what you'll see on the petrol pump is usually the "mean" octane number - notified as (R+M)/2 - the average of both the RON and MON. This is why there is an apparent discrepancy between the octane values of petrol in America versus the rest of the world. Euro95 unleaded in Europe is 95 octane but it's the equivalent of American (R+M)/2 89 octane.
In America, low altitude petrol stations typically sell three grades of petrol with octane ratings of 87, 89 and 91. High altitude stations typically also sell three grades, but with lower values - 85, 87 and 89.

Source: Car Bibles: Fuel and Engine Bible

**JackFlash** · December 7th, 2012 12:16 PM

Originally Posted by Alpha_One

The answer is quite mundane, actually: The US does not use Research Octane Number (RON) to measure octane rating, but the Anti-Knock Index (AKI). 89 AKI is roughly equivalent to 95 RON. In other words, more or less they get exactly the same fuel that we do.

Source: Car Bibles: Fuel and Engine Bible

So that explains it. Thanks very much!