Ask any driver where they get their gas, and you’ve opened a deep discussion. There are the few that get it from wherever (including the canteen in the back of their trunk because they always run out,) but most drivers have a preference.

The first question is, “Where do you get your gas?” Do you go for the cheapest gas station you can find, or go to the expensive places because it must be better? For that question, it seems that there really isn’t a difference:

A joint study by ABC News and the Maryland State Comptroller’s Office examined the difference between name brand and generic gas. Chemists at the Maryland Fuel Testing Laboratory conducted a battery of tests: They verified that the gas was formulated correctly for the season, checked for contaminants like excessive sediments or diesel accidentally mixed with the gas, and they ran the gas through an elaborate engine to ensure that it was all the same 87 octane level.

Here’s some good news for consumer: Regular and discount gas are basically similar.

“By and large, it’s one and the same,” said Bob Crawford of the Maryland Fuel Testing Lab. “You will find results will almost mirror each other. There are going to be slight variations, but gasoline is gasoline."

The primary difference between competing brands is the amount of detergent the distributors add to it. Even still, the difference is generally minor: The EPA requires all gas to have a minimum amount of detergent to keep a car’s engine clean.

“You would be paying for brand loyalty, primarily,” said Crawford, explaining why brand name gas costs more. “Some people feel more comfortable dealing with a particular brand."

Crawford, who has been studying fuel for 36 years, uses whatever gas is the cheapest. Some cars require premium gas, but generally, regular is fine.

That last quote raises a good point. If the choice of station really doesn’t make a difference, what about the octane? Some cars explicitly require Premium gas, but what about the others? Just as with software, the only way to be sure about the value of your gas is to measure it.

For example, I used to drive a 1998 Hyundai Accent. I gave it the cheapest gas, because it didn’t deserve any better :) Then one day, I tried Super Premium Ultra Deluxo gas on a lark, and got 19% better gas mileage.  Since premium fuel is only about 9-10% more expensive than dirt cheap fuel, it is well worth the money. So I turned into one of the people I used to laugh at: dumping super premium gas into a car with 107 HP.

It really comes down to figuring out the gas that gives you the best “miles per dollar,” and stick with it.

(Miles per dollar = Miles per Gallon / Dollars per Gallon)

The exact mileage you get from a given fill-up is easy to determine. Reset your trip odometer to zero just after you fill up. All the way up. The next time you fill your tank, make sure to fill it all the way up again. The pump will tell you how many gallons it gave you. Then, divide the measurement on your trip odometer by the number of gallons you just put in the tank, and you have your car’s mileage from the last fill up. Then, reset your trip odometer and start again.

Different octanes may have an effect on Miles per Gallon for your car, and will most definitely have an effect on Dollars per Gallon. Using the same octane from different suppliers may have an effect on Miles per Gallon, and will probably have an effect on Dollars per Gallon.

So, to figure out the best fuel for you, make a simple chart:

For the Dollars per Gallon number, make sure to use the real price. For example, AARCO AM/PM adds a 45-cent surcharge per tank, which increases their advertized dollars per gallon by about 4 cents per gallon.

Experiment for awhile, and settle on the place that gives you the most Miles per Dollar.