This could be one reason why MPG figures have such a variation. Here in AZ 1 in 50 stations were found to be giving short measures. Add that to the MPG loss due to lower octane fuel and subsquent timing adjustment by the ECU and no wonder there is so little consistancy to MPG numbers. If you use the same station all the time you might be cheated, but it will be repeatable, for people who travel around and fill up at different places the mileage will be all over the place.