Mobil 1 "European blend" 0W40 is an acceptable substitute for the BMW oil.

Heck, at the 6000 mile interval that I'm changing the oil, probably any synthetic is OK. You only really need "the good stuff" for extended drain intervals.

I used Mobil 1's ATF fluid in the transfer case and transmission, and their synthetic gear lube in the diff. I've got an '02, so no X drive.

FWIW, the oil in the transfer case and diffs was clear and looked good. Perhaps it did not need to be changed. The transmission fluid was black and very dirty.

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'02 X5 4.4i