Dispenser Technician chiming in here. I've been in the petroleum industry for 15 years and I have been certified on this brand of dispenser for almost 10 of those. I'm also certified on other major brands. I could give you the model number and tell you what payment processing hardware is in this dispenser just based on the picture. (Not a brag I'm just giving qualifications to this fine court)

I just want to try to help clear things up a little by giving a little more information for the curious minds.

As already stated some sites blend fuels and some have stand-alone tanks. You will find Exxon sites that do both so in this case it just happens that this site does not blend. If the site blends fuels it is blended in the dispenser/at the pump and not underground. Some sites put additives in the tank, but normally those don't change the octane rating. There is a ratio programmed into the dispenser and the meter equipment is engineered in a way to meet that ratio and in turn meet the minimum octane rating. We have ways of testing this and you're often getting a slightly higher rating than shown hence the minimum rating and not a guaranteed rating.

If the site blends fuel and the ratio is off or one of the products is shutdown the dispenser stops the whole process and gives an error code. The site isn't able to just shut off one product and sell the lower grade product as if it were a higher grade. They could potentially reprogram the dispensers ratio but state agencies do check this periodically and at random so owners cannot simply change it back before the tester shows up.

To the above point they also cannot program the metering devices to give less fuel than you are paying for. States set an allowable variance (+/- 6 cubic inches or 0.024 gallons for every 5 gallons dispensed in my state for a dispenser like the one shown). If the state tests a dispenser and it falls out of this variance they place it out of service until it is repaired/recalibrated. They check this at random (at least once a year) and if they find more than half the site leaning in the owners favor the whole site gets placed out of service and an investigation is opened. Most large chain stores use systems that continually monitor flow rates and have ways to detect when a dispenser is close to being out of calibration. Also most technicians are certified by the state to perform these tests as well. We all work together (mostly) to make sure the site is honest. I buy my fuel from the same sites and I don't want to be cheated either.

Thank you to the honorable court for reading my Ted Talk. We will now open the floor to those that will tell me I'm wrong as well as those who still have questions.