Oil

An engine can burn oil, you might see blue-tinged exhaust smoke in that case. A leak down test might reveal blow-by in the piston rings or valves. Keep an eye on oil level until you make repairs, don't run the motor with it too low.

If there is none on the ground either somebody is stealing it (not very likely) or it is going out the tail pipe. Sometimes today's cars can burn quite a large amount of oil before smoke appears at the exhaust pipe. How many miles and which engine on this Charger?

It may be leaking oil from the back seal. Because when you have a back seal leaking it's between the transmission and engine it will only leak while you're driving it. That's why your oil runs low quick and you can't figure out where it's going when you don't see any leaks while it's parked.