Octane rating vs age of Petrol

[Alpine]

I have read numerous times on the forum that 98 octane petrol gradually deteriorates over time and its octane decreases as a result, eg 98 will become 97, 96, 95 over time and so on.

So how about good ol' regular 91 unleaded? Is 91 subject to this same deterioration over time as well? Does anyone know for sure?

[aaronng]

If you have 98 RON and let it sit for a month, it will probably still be above 95 RON after that. I didn't feel anything different.

[IZY-10]

my theory is that petrol looses 1ron per month. Not to sure if that is true though

[SeverAMV]

chemically its impossible for the octane rating to just decrease. if it does, its not the fuel itself but the additives in it causing it to decrease.
if your fuel is exposed to oxygen and let to rest for a while without being used, oxidation can occur and convert octane into octanol, or octanoic acid. these can corrode any metal lines slowly, however, they do not reduce your octane rating. in fact, they actually increase it, as they are more oxygenated and improve complete combustion rate and combustion efficiency, and hence improve power.

[aimre]

my theory is that petrol looses 1ron per month. Not to sure if that is true though

anything to back that theory up?

[IZY-10]

no just browsing around the forums and that seems to be the average

[Alpine]

Nobody has mentioned if it also affects 91 regular unleaded yet...eg if it drops to 90, 89 etc. like Ultimate, Optimax, etc.

[aaronng]

The only time you will come across this issue is if you are going overseas for 2-3 months at a time. By that time, petrol is the least of your worries. I'd be worried about the tyres developing flat spots, engine oil needing to be changed and probably the coolant too.