Depends on where you're from BJ....if you're in the US, use Mobil 1 15w50 synthetic extended service (15000 mile oil). But change it at regular intervals and not at 15000..=)
I just changed the oil in my M5 yesterday, I found 6 quarts of Mobil 1 15w50 synthetic at Target for $2 a quart on closeout, the parts stores get over $5 a quart.
If you're looking for "Dino" oil, you still need at least 15w50...