Anyone driving his/her vehicle on a regular basis is concerned about its fuel economy While many older vehicles were not very fuel efficient, it is in the interest of both the owner and the environment to ensure that the vehicle consume as little fuel as possible It is useful to keep a fuel consumption records to have a baseline for the vehicle's expected fuel economy and to have some indication of developing problems.

Often drivers recall their fuel economy from memory but, without circumstances and data, this can be misleading Some factors that could make today's fuel economy different than historical reality are:

  • Recollection of only one particular trip
  • Incorrect fuel economy calculations
  • Calibration of odometer (tires/axle gear/odometer gear)
  • Deterioration in mechanical condition
  • Variation in gas tank fill amount level
  • Variation in fuel's energy content [eg, 100% gasoline vs E10 (gasoline with 10% ethanol)]
  • Variation in average vehicle speed