I have 2000 S80 2.9. I changed motor oil five months ago and I only drove 2,000 miles.

yesterday, I realized the level of engine oil is too low.
so I just added 1 quart oil. yes, the indicator of the dipstick is higher than before but it's still under a max mark. I just stopped to add oil because the oil level is between min and max marks on the dipstick.

My question is
what's wrong with my car? I think I don't have oil leak problems because there is no stains underneath of my car.
The oil can be burned out about 1 quart? 1 quart oil is large quantity. is it possible? I've never noticed burning smell coming from the air vents.

any comments and suggestions are very welcome.

Thanks in advance,

 

Remember that not all oil leaks are visual, on my accord I couldnt figure out why the level was dropping cosidering I wasnt burning oil... it was internak leaks around the spark plug seals, so sometimes you have to look inside to figure it out...

Right now my Volvo clearly has a rear main (rear crankshaft) seal leak, and its only getting worse and worse.. to the point where I managed to lose about 3 or 4 qt's on a 500 mile road trip...