[Draper]

Nope. Can't use E85 on a stock X5.

There may be a conversion kit around, but BMW's official stance is they don't recommend it.

Contrary to some info floating around, 'good' E85 tops out at about 94-97 octane and not 105 octane. Also, this octane rating will decrease substantially within a relatively short time as the fuel ages, so if you buy from a station with old E85 (no way to tell) you'll get a lower octane than you'd get with normal premium.

To top it all off, E85 gets about 30% less mpg than regular fuel, so unless you're local price is >30% less expensive than premium it's not even a good value.