[TKWPrime]

You are correct. Filling up with different pumps will average out over time. The original poster was talking about filling up with two different brands and noting a mileage difference and I was pointing out that the difference could be entirely due to errors in measurement.

Another point. Supposed he filled up with Brand X and drove 300 miles on a calm day. Then filled up with Brand Y and drove 300 miles but it was into a 15 mph headwind. Without allowing for the wind, it would appear that Brand X gives better mileage than Brand Y.

Now, if you keep very careful records about which fuel (and pump) you use on every fillup, record the weather and road conditions, etc. You really can't conclude that one brand of go-juice is really any better than another.