Having oil in the air filter usually is caused by a bad PCV valve (Positive Crankcase Ventilation Valve) and can be fixed by simply replacing the valve.
To check to see if you have a bad PCV valve, remove the valve from the rubber grommet in the valve cover and place your thumb over the valve with the engine idling at normal operating temperature.
You should be able to feel a vacuum. If no vacuum is felt, turn the engine off and shake the PCV valve and listen for a rattle. If you don’t hear a rattle, replace the PCV valve with a new one.
While it’s not uncommon to have a small amount of oil in the air filter, excess oil could mean bigger problems than just a bad PCV valve.
As engines get older and start to ware you will get what is called “blow-by” this is caused by worn rings that allow excess pressure to build up in the crankcase and will force oil past the PCV valve and into your air filter.
If this is what’s causing your oil in the air filter, you may be looking at having to rebuild your engine.
It would be wise to take your Jeep to a qualified mechanic to have your engine compression tested to see if you are starting to have ring or valve problems.