Yeah gasoline doesn’t keep very well.
I think diesel has a good shelf life if you put the proper additives in. I used to work at Allison, we had to put a biocide in our automatic transmissions because if they sat in inventory a long time, you could get algae growing in the lube oil. Diesel can do the same thing.
https://www.grainger.com/product/STA-BIL-Diesel-Biocide-32EY89
Yeah, I was just reading up on storing diesel the other day. Still have the tab open, which makes it all the worse that I didn’t grab that little plastic drum. Two 5 gallon jugs and fill the tank. Ought to last a while and I won’t have to mow for a while. It’s a sub-compact Mitsubishi tractor with a 3 cylinder.