oil usage

a post I put on earlier was moved to the detailing section , the brown spots on the bumper appear to be coming out of the exhaust , as your driving along in any car a vortex is created and if anything is coming out of the exhaust it can settle on the rear of the car , that's why the back of a car in heavy rain gets ditched . my worry is that it may be oil or unburnt fuel , I have had to top the oil up more than I would have expected since the last oil change . about 2 litres in 5000 miles . has anyone experienced the same?
 
a post I put on earlier was moved to the detailing section , the brown spots on the bumper appear to be coming out of the exhaust , as your driving along in any car a vortex is created and if anything is coming out of the exhaust it can settle on the rear of the car , that's why the back of a car in heavy rain gets ditched . my worry is that it may be oil or unburnt fuel , I have had to top the oil up more than I would have expected since the last oil change . about 2 litres in 5000 miles . has anyone experienced the same?

Has the car had the cats removed? I'm sure someone will give the oil consumption tolerance later.