Worn valve guides or piston rings is the most likely cause. An engine that is burning oil will show signs of blue/gray smoke coming out the tail pipe when you first star the car in the morning? If so it would be a sign of worn valve guides or valve guide seals.Worn guides or seals may also exhibit being a problem if after prolonged idle at say a traffic light, when you pull away blue smoke is emitted from the tail pipe. Get a friend to follow you on the freeway on hard steady acceleration is there any "blue" smoke out the tail pipe, this would be a sign of bad piston rings, damaged pistons or a worn engine cylinder bore. Some engine oil "burning" is acceptable. I saw one manufacturer say they would not even investigate an "oil consumption problem" on a brand new car if it was not more than 1 quart every 800 miles. That to me is unacceptable! Their is a test called a cylinder leakage test where compressed air is put in an engines cylinder with its valves closed to determine if an engine has cylinder head gasket, intake or exhaust valve, or worn piston rings/cylinder bore. It is a very valid test to determine the over all health of an engine.