Thanks JCL. In my area diesel goes for abou $3.85 while super runs about $4.10. Since BMW recommends a minimum of 91, the fuel price is a bonus along with the mileage. When you say water in the fuel and filter replacements, are the filters easier to change since it might be done more often? Also, I've been using Mobil 1 0w-40 for my wife's current X5. Can I still use the same oil (when the warranty expires)? If there's water in the tank, is it ok to put a few bottles of gas dryer (that yellow bottle stuff) or will that harm diesel?