Jet fuel will weather over a period of time as noflynomore describes. If returned to low altitude (generally back on the ground) will reabsorb air from the atmosphere over a period of days or weeks after having been taken to altitude and thus degassed.
From my rather hazy recollections, air in fuel exists in three states. The size of the groups of molecules and their degree of entrapment by the fuel determining the boundaries between the types.