How much fuel are you caching?

[JD1]

I use Sta-bil and it states it is good for 12 months at the standard dosage or 24 months with double the dosage. Adds about 20p per litre to the price of the fuel but worth it.

I haven't stored any longer than the recommended length of time so cant vouch for the following, but a bloke on another forum said he tried some treated petrol after 5 or 6 years and it was fine