IIRC, there are two grades of commonly available fuel in the UK, 95 RON and 98 RON. They correlate (approximately) to 89 AKI and 92 AKI, since the US uses the pump octane method and the UK uses the Research octane method.

I checked back to see if I had missed something in the original post. Nope, nothing there about price. So why did recent posters turn this into a thread about saving money or complaining about gas prices? It was a question about whether people used other than premium, and if so whether they had problems.

Second observation is that a number of people report using 93. There are two possible reasons that I can guess: Either people have very bad quality fuel where they live and they need to buy 93 to actually get 91, or they believe that an AKI above that which is required is somehow a benefit to their engine (it isn't). Am I missing something? Is 93 all that is available? (We get 87, 89, 92, 94 at the pumps).

Always! Using Shell exclusively and found improvements in all driving conditions, and my fuels gauge no longer 'sticks'. Whenever I was forced to take lesser octane (or that ethanol crap), mileage dropped 3mpg(or more).

High elevation, gas is 85, 87, 91
In New Mexico, the best I could get was 90
sea level is normally 87, 89, (92,93,94)

91 is not too common here - where I live in MA most pumps have 87, 89, 93 so 93 it is for me.

around where i live, they offer 92, 93 and shell ultra offers 94 at a premium.

As a rule of thumb, I generally get premium for the cars that need it, and 87 for the one that doesnt. The 87 car actually gets the most miles on the road ;)

Exactly! Same here... Especially in full service NJ, I just say "93" instead of looking to see what they have...

If you are getting knock (detonation) then you need more octane. If you aren't then you do not. You can probably cruise successfully at lower RPMS (too bad my manual trans doesn't really do that) with lower octane but if you get into the throttle your cylinder head temps will rise and you probably will get pinging. The ECU will try and compensate for this over time and add fuel to the trims, but eventually even that will not work if you are running the engine hard, or if you have a secondary problem like too much blowby in the intake (seperator problems, anyone?) or your plugs are fouled. Not to mention the computer adding fuel will use more gas, and therefore cost you more, which I supposed is why you are even asking this question in the first place. So that is counterproductive.

The compression ratio of the heads and piston combination was designed for a reason, and that is performance. If you do not use the performance, you may not need the corresponding octane, but if you want the performance, you need to run the correct octane to prevent knock or pre detonating the charge.

WE have 87 89 and 9x depending on the retailer. My 3.0 pings with the lower two grades under heavy accelleration, and my fuel trims get pig rich on 87 under all operating conditions. I run 9x.

Where I live, there is 87, 89, and 91 (But I've never been to Shell).
I used 87 a couple times and a them same times my car wouldn't start up later.

Took it to the mechanic and they couldn't figure out why. Ever since, I've used 91 Octane and it hasnt not started :D

I dug this thread out just to read on others experiences. I threw 89 in my X5 the other day just to “see” what would happen (knowing the recommendations in the manual and fuel door). For 300+ miles she knocked and pinged, idled ruff, accelerated slowly and performed poorly to say the least.


Today I filled her up with 93 and she was right back where she was before, a high performing, smooth driving monster.


I’ll NEVER do that again and I don’t recommend it to anyone!

If you have a chip/sharked the vehicle you absolutely want to use premium as the change is designed to produce higher hp out of the higher octane by changing gas/air compression ratios. Throw 89 in there and expect some nice engine ping.

I have had three e36s and every one of them had gas mileage also increase as a result of chipping/sharking. These are ODBIs and ODBIIs. Considering today's gas prices and the smaller price difference in plus to premium, it may be worth considering especialy if you are using premium like most manuals state anyhow.