I used AMS oil 0W-40 European Spec in my E38 750iL (owned for 6 years) and E36 328i (owned for 5 years) with no issues at all. I can't say there was a mileage improvement because that really boils down to is the car being used as intended (such as when I get 23 mpg out of the 7 cruising at 85 mph in Nebraska).

I just change the oil for the first time in the E60 (new car warrenty and included maintenance expired) and have had no issues thus far.

 

Why bother - most BMW Dealers list monthly specials like this one (PS not my dealer but I did a quick Google search)

http://www.bmwatlanticcity.com/specials/parts.htm

 

Ok, thanks, it's now clear why AMSoil is not BMW "recommended". Gotta pay to play.