Don, I was given some old K&B {I think} fuel that was stored under A bench for well over 15 years and the stuff worked just fine. About 10 years ago I found A couple of pint cans of Thimbuldrom {spelling} fuel that I had boxed up with my Prop Rod when I was A kid. That fuel was over 37 years old, worked just great in my 1/2 A glider engine.
Unless the fuel gets water in it the stuff doesn't break down. That 1/2A fuel had moved from So. Cal. to the mountains before I found it again so it traveled A long road before it got used!!

I agree with the others that sealed jugs should be good for a long time. I just used a can of Powermaster that was a fun-fly prize from 5 years ago and it ran fine.

If I was not positive that the "old" fuel is good, I wouldn't even consider mixing it with "new." If it is "bad," and you mix it with "good," you end up with two gallons of "bad" compared to having one of each.

Hi

Even if fuel did have water in it you can freeze it and then drain the unfrozen fuel off theoretically.

Same concept as wine that has gone off to extract the alchohol.

Never tried either though.

Simon

Our club got some old fuel that looked like from the can's condition it was over 20 years old and the club's trainer flew fine on it. We just made sure we had a filter on the inlet line as the can was rusty!