Heck, as much as you want to if you keep your yap shut. No tell no-bhady, keep moufy closed. For best amount of storage for the floor space, I think the 10.5 gallon flo-fast cans are the shiznit. You can get the 14-25 gallon caddy types, but they are more complex and harder to handle. The Flo-fast cans are hella tough, and more managable to me. Also, you can split the cans up for better survivability. I DO NOT like the fuel caddys with the bottom hose connection. Get a leak there, and not only can you lose about your whole gas load, but then you have an entire garage full of explosive, extraordinarily flammable liquid.