For the last 18 years, I have kept a record of fuel consumption in a spread sheet of the cars I have driven, from 1997 to 2002 when I drove company cars. After I retired I kept the spread sheets going. I always base these on tank full to tank full checks since average mpgs from trip computers are notoriously optimistic. Having suffered the cost of replacing the diesel turbo on my Jaguar X Type earlier this year, I decided to run on Shell V Power Nitro diesel, initially in an effort to avoid a repeat of turbo failure . In addition, from a detailed analysis across 2,000 miles on each fuel grade, I have recorded a 7.5% increase in mpg using V Power Nitro.