You can buy "petrol preservative" which stops your petrol from "going off". You may not want to use the petrol in your beaut ute when it's been sitting there for some time, but you could probably use it in something #OOPS#ty (like, say, a commodore). Anyway if you added it before you stopped driving it it could be in the petrol in your lines, pump, filter and carbies as well as the tank and that would probably be a good thing.
I seem to remember that I've seen it at the mower shop!