It's something few of us think about when pumping gasoline- where is it stored, and how is it delivered to my gasoline tank?
Gasoline stations typically have at least two large underground storage tanks for gasoline- one typically contains the lowest octane gasoline (regular grade) and one typically contains the highest gasoline (premium grade).
After you select what type of grade you want to purchase, large pumps attached to or in the underground storage tanks begin pumping gasoline to the dispenser and into your vehicle. If you purchase mid-grade, did you know that the dispenser simply blends premium with regular? It does so with something called the blend valve. This valve can mix different amounts of different octane gas. This is why some stations can offer as many as five grades with just two main gasoline tanks. To get to the advertised octane rating, the blend valve simply blends less premium gasoline into regular gasoline.
For more reading on how gasoline gets from storage tanks into your vehicle and all the cool stuff you didn't know about gasoline pumps, dispensers, and how things work, be sure to check out
the How Stuff Works article on gas pumps!