car using oil

My 2002 subaru outback wagon 4cyl is using oil. There are no oil marks on the pavement where it is parked. There is a slight smell of oil when I walk by the front of the vehicle after turning it off. No visible oil on the engine block. When I checked the oil yesterday it did not register on the dip stick. I put 2 quarts in before it registered. No oil light came on. There is no smoke coming from exhaust or tail pipe. Any information would help. Would like to be informed when I take it in to get checked. Thank You, Tom A. Omaha