We keep a 500 gallon gas tank for the farm. I rarely keep it full because we don't use enough gas before it gets old. There is also the problem with winter and summer blends of both gas and diesel. The wrong blend in the wrong season will not run as efficiently. While there are additives that will extend the storage life, it does not store indefinitely.I could upgrade to a 300 gallon gas container.
When the power was out for 2 1/2 days I went through 46 gallons running two generators.
My Honda 4-wheeler averages 42mpg just riding. If I start really working it, that can drop below 30mpg quickly. Pulling the mower I can mow our 10 acres on about 1.5 gallons.
I've used the Polaris Ranger to pull the mower, but not often because it will burn through 5+ gallons covering the same area as the 4-wheeler.
On the idea of an EMP event?
There will be bigger problems than whether my ATV's still run, although I've read that equipment stored in aluminum or steel buildings have a better chance of surviving. Not sure how true that is, but both of my shops have steel roof and siding.
If it ever happens I'll let you know. Or not... >;~}