Fuel turns to vapor, and if you burp the can or tank after it sits, the O2 goes away. Cars self purge through the evap. system.
Pretty much the reason cars don't explode when in tank fuel pumps short out. I've pulled pumps out where the wires have actually melted inside the tank, sometimes enough to burn a hole in the plastic sending unit (module). If the tank had O2 in it, the car would at the least start on fire if the tank was low.