Got to watch those stations were you fill up (say 16.5 to 17 gallons). The station may not have totally accurate pumping units.
If you are putting in that much the pump might need calibrating.
Looks to be the station is cheating you out of some gas. [you by 16.5 gallons and only get 15. Station make out like a bandit.]
I'd stay away from this station, He gets richer and you get ripped off.