I have participated in a few discussions on this forum concerning whether the 15K oil change interval recommended for new BMWs is adequate. I think it is fair to say that most owners voicing their views on this are skeptical and somewhat suspicious about such a long interval. After driving my 2004 745li for about 12K miles after its last oil change, I sent a sample to Blackstone Labs for an oil analysis. The results were shocking -- a lot of metals in the oil and total exhaustion of the protective oil qualities. So I concluded that perhaps those who warned that 15K was too long were right. Well, I have thought some more on this point. And the following occurs to me: 1. The longer the oil interval, the more metals are likely to accumulate in the oil, even if the oil is NOT failing in its ability to lubricate the engine. It seems to me that some metal will accumulate in the oil and the more time between intervals, the more accumulation. But that does not necessarily mean that the oil interval is too long. 2. The idea that the protective qualities of the oil are "exhausted" seems to me somewhat ambiguous in the context of an oil analysis. Not sure what it means. Certainly the oil will change in chemical composition over time. But the question is: What material effect will this have on the engine. The oil analysis assumes that the effect will be deleterious, and that is plausible. But at what rate? If I had kept driving the car to the recommended 15K limit, would that have made a significant difference in engine wear? So I would say my current frame of mind concerning these long recommended intervals is one of -- well, confusion. It is extremely wasteful and potentially harmful to the environment to change oil too frequently, and it is harmful to the engine to delay changing it when the oil needs changing. But I am not sure the oil analysis is the definitive test I thought it was. Interested in other views on this subject.