Here's my observation when I switched oils. I've been using castrol 5W-30 for a few oil changes with the X5M and found that I needed to add a quart every 800-1k miles. I tried Mobil 1 0w-40 and my oil consumption dropped to 1 quart every 2,500 miles. I'm now using Liqui-moly 5w-40 and reached 2k miles (3,218 kil) and the oil level shows 3/4 full.

The car is driving hard daily...basically do an "Italian Tune-Up" everyday.