I've run my 330i under original warranty very close

to the 15K mile mark for oil changes (3 oil changes to 45K miles)as recommended by BMW using the BMW oil. What exactly is BMW oil? I've never had to add oil between changes. After it went off warranty at 50K miles I did the next change myself. The oil looked about the same as any I've ever changed. I also don't think you can tell a thing from the looks of the oil. I've not experienced any problems. I'm going to switch to changing now around 8K to 9K intervals just because it works out to be about 2 changes/year on this 90% highway miles, mid GA, vehicle. There are many factors to consider in choosing a change interval. Superstitious owner preference, ranks as high as any other factor. The owner must be comfortable with the choice of interval. Other considerations might be engine type, age,
fuel delivery system (carb or EFI) miles, type of use: highway, city, off-road, racing, seasonal environmental conditions, temperature, humiditty, etc..