Is all gas the same?
Gas is gas until just after it is loaded on your local tanker truck.
You see, the way the gasoline distribution works is actually quite scary. The oil is brought to the refinery and is of course refined into many different products and then stored until it is pumped into massive pipes that carry it to distibution facilities around the country. Sound simple? Well, it's actually a very complicated and computerized switching network.
Let's say exxon is scheduled to upload gasoline into pipeline #125 between 3pm and 5pm one day. They may pump 100,000 gallons of premium then follow it immediately with 100,000 gallons of regular (yes, the 2 grades will mix but this portion of the load is used by factories and other places where the grade is unimportant, didn't know that did ya!). Anyway, at the distribution facility, Shell may actually get Exxon's gasoline from the other end! The additives are not added to gasoline until the last minute when the fuel is being loaded into those 18 wheel tankers you see on the road.
To make it simple, all the refineries put in and they are allowed to take out whatever they put in......in fact, more often than not, the gas that they take is not theirs....
As a sidenote, before computers and precise computer controlled valves, "pigs" were used to seperate the grades of gas...These were huge chunks of rubber or other material that was inserted into the pipeline and removed at the other end....they are actually still used to clean the pipelines.
Bottom line....the only difference in gasoline is the type and amount of additive added at the end......
(information courtesy of JC)