I have been crusing through this site and noticed there is a lot of misinformation and confusion about oil. Here are a few things you should know about oil for BMW's:
1) All new BMW's require synthetic. As far as weight, only certain production dates of M3's and M5's require the use of Castrol TWS 10w-60.
2) The Factory BMW Synth 5w-30 is a version of Castrol TXT Softect sold overseas. A few important things about the BMW oil a) it is a Group III hydrocracked oil which cannot be called synthetic in Europe, b) it is a heavy 30 weight (30 weight can run from 9.3-12.5cst@100c, the BMW oil is about 12.2cst), c) it is a ACEA A3 oil which means that it is approved for longer change intervals and has a HTHS (High Tempurature High Shear) measured at 150c of greater than 3.5.
3) In the US, the only Group IV PAO Synthetics that are available are 1) Mobil 1, 2) Amsoil (but not the Xl-7500), 3) Royal Purple, and 4) German Castrol 0w-30 (it has the red label and says on the back, "Made in Germany). Redline is a Group V PolyEster based oil. All other Castrol, Quaker State, Pennzoil, Valvoline "synthetics" are a Group III hydrocracked oil. It is debated how much better Group IV base oils are than group III, but generally they are considered better.
4) When looking for oil for any BMW that does not require Castrol TWS 10w-60, you want to purchase an oil that has either/both of the following ratings, a) ACEA A3, or b) BMW LL-98 or LL-01.
5) Note that Mobil 1 0w-30, 5w-30, and 10w-30 are NOT ACEA A3 or BMW LL approved oils. This is because they all are thin 30 weight oils (approximately 9.8-10 CST@ 100c) and have HTHS of approximately 3.1. Mobil 1 0w-40 and 15w-50 are A3 rated and the Ow-40 is BMW LL-01 approved. For 99% of climates and users 0w-40 or 5w-40 is the appropriate grade. There are some 0w-30 and 5w-30 oils (like the BMW 5w-30) that are forumlated on the heavier end of the 30 weight scale and are accordingly rated A3. These oils will work well also. LOOK FOR THAT ACEA A3 rating. If the oil doesn't have it, pass on it.
6) Some people seem confused about how oil thickness is measured. The first number (0W, 5w, 10w, 15w, etc) is a measurement of how thick the oil is at tempuratures of -35c- -20c (depends on the grade). The lower this first number the thinner the oil is at LOW tempuratures. The second number (30, 40, 50) refers to oil thickness at 100c (operating tempurature). 30 weight can be from 9.3-12.5 cst, 40 weight from 12.6-16.2 cst, 50 weight from 16.3-22cst (approximate). So you can have two oils, one called a 5w-30 (i.e. bmw oil) another 0w-40 (Mobil 1) that are very similar thicknesses at operating tempurature. Compare this to Mobil 1 Xw-30 which is close to a 20 weight oil at 100c. For more information here is a link with exact numbers http://www.bobistheoilguy.com/visc.html
7) BMW's recommended interval of 12,000-15,000 miles is to long. Used oil analysis has shown the BMW oil is generally depleted at 10,000 miles. Running it longer results in excess wear. It is highly recommended that you change your oil once between each BMW recommended interval (approx 7000-7500 miles). If you want to run your oil the BMW recommended interval, I would suggest that you use Mobil 1 0w-40 or Amsoil 5w-40 and change the oil filter at 7500 miles. I would encourage a full oil change at 7500 if you want your engine to last.
8) If you want to spend a few hours learning about oil, go to bobistheoilguy.com