Fuel

[Farmboy444]

I recently did a little test of what type of fuel yields me the best mileage. I Knew what I was getting off of Road fuel, 15 around town. A friend who runs off road fuel in his 99 always says that he gets worse mpg on off road. I have ran a good bit of farm fuel but never paid attention to mileage. So i filled up with off road fuel at the station and tracted mileage, i got 12 mpg off farm fuel 3 miles less per mile. How does this happen. I thought that farm fuel would have a higher sulfur content, hence better economy. I dont understand it