I'm pretty sure it's well known that BMW oil is the same as Castrol Edge Euro oil. there was a thread I started a while back and some one proved this to be the case.
If you care to read, here's link to a technical description of different grades of motor oil: http://www.upmpg.com/tech_articles/motoroil_viscosity/
. It speaks favorably about Mobil 1 Euro 0W-40, which happens to be a BMW approved oil.
2012 Z4 35i, ED 2/24/2012, Melbourne Red Metallic, Black Leather, Carbon Trim, 6MT, ///M Sport, CW, PP, PS, NAV, CA, LED Angel Eyes, red calipers, pedal covers, stubby antenna, Luxon strut bar, CF engine cover, LCI side markers, 35is mufflers, Extra Enjoyment Package.