I actually did this calculation to determine which was better for fuel economy. Here are the numbers that I could calculate. If anyone sees any discrepancies, please let me know.
 2011 X5 35d (1)  2011 X5 35i (2)  L/100km  MPG (*)  L/100km  MPG (*)  City  10.7  22  13.2  17.8  Hwy  7.5  31.4  8.3  28.3  Combined  9.3  25.3  10.1  23.3  EPA Cost per year (3)  $1,741.11  $2,141.09  CDN Cost per year (4)  $2,119.30  $3,008.20  Distance per tank  568 miles / 914 km  523 miles / 842 km 
Notes on numbers:
(*) The MPG numbers are converted from European L/100km to US MPG. I couldn't get the 35d numbers to match the 19/26 that the EPA suggests for the 2010 35d and since I couldn't find EPA numbers for 2011, I converted from L/100kms that could be found.
(1) From specifications at the http://www.bmw.ca website. In the Canadian 2011 X5 press release, the highway fuel economy was mentioned as the same as the 2010 so I am assuming the same numbers.
(2) From Specifications of the new BMW X5, 04/2010 which are European specs but are the the same as Canada.
(3) Based on EPA's Cost/Year formula of 45% Hwy/55% City for 15,000 miles per year where gas is $3.05 per gallon and diesel is $2.95 per gallon. DEF NOT included.
(4) For comparison, sort of based on EPA's Cost/Year formula of 45% Hwy/55% City for 15,000 miles per year where premium gas today is $1.132 per litre and diesel today is $0.949 per litre in Toronto, Ontario. DEF NOT included.
Last edited by santo; 03252010 at 11:53 AM.
Reason: Added distance per tank
