Quick hits from Google:

http://www.grmotorsports.com/backissues/biodiesel.php
^ BMW racer in 1985 running Bio-Diesel

http://www.discoveralternatives.org/...Technology.php
^ What a car can generally run without changes to fuel components.

There isn't really anything particular that says the X5 can run it. So unless you have tons of cash laying around to replace the motor components, I wouldn't do it.

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