[K.P.]

There's a product called Sta-Bil that you can add to petrol to stabilise it and it won't go off for a year but it isn't cheap, about $28. I'm not sure the alcohol evapourates...it attracts water which then separates from the petrol. You'd think some of the alcohol would evapourate too, but maybe not.

I've heard of the oil in the petrol trick but would a car appreciate it?