Mine is a petrol 2.2 and uses about a liter in a thousand miles. As for where it goes, some say it shouldn't use any, but by my reckoning that has to be a bit of ********.
Oil is the engine lubricant so some *must* get used even if it's a tiny amount and some will get swiped up the cylinder walls every stroke of the pistons and then burnt off the cylinder walls every combustion cycle, so even the smallest amount *has* to be burnt off. With the miles going on, the piston rings wear and wear so more oil's used to lubricate the pistons,so the oil useage increases... and that's just one example