The average price of regular gas this week is $2.57 -- lower than a few weeks ago, but still far more than Americans are used to paying. As some drivers turn to generic gasoline from no-name stations to cut costs, "Good Morning America" investigated whether generic gas is good for your car.
With the help of the Maryland State Comptroller, ABC News compared gas from a name-brand Mobil station and a generic Liberty station right across the street from each other. Mobil was charging $2.69 a gallon for regular, while Liberty charged $2.49 a gallon.
The comptroller's office collected samples of regular unleaded at each station. The inspector followed a strict protocol, flushing the line between samples and carefully labeling canisters.
At the Maryland Fuel Testing Laboratory, chemists conducted a battery of tests. First, they verified that gas was formulated correctly for the season. Then, they checked for contaminants, like excessive sediment or diesel, accidentally mixed with the gasoline.
They also ran the gas through an elaborate engine to make sure it got the 87 octane level people pay for. Both samples easily met state standards.
"By and large, it's one and the same. … You will find results will almost mirror each other," said Bob Crawford, who works at the lab. "There are going to be slight variations -- but gasoline is gasoline."
When gasoline arrives at regional distribution centers, it's all the same. Different gas station chains then buy the raw fuel and add their own blend of detergents. In the past, there might have been more of a difference between different brands of regular unleaded, but these days the EPA requires that all gas contain a minimum amount of detergent to keep car engines clean.
If you're paying for a particular brand of gasoline, "you would be paying more for brand loyalty, primarily," Crawford said. "Some people feel more comfortable dealing with a particular brand."
Many customers keep coming back because they use a particular name-brand station's credit card.
Some generic stations only take cash, which is one way they keep prices down.
"The generic, no, will not do harm at all," Crawford said. "I use the lowest price. It makes no difference what the brand is."
There's no easy way to test for the quantity and type of detergents in gasoline, because those formulas are trade secrets.
Ewing Oil, the company that supplies gasoline to the Liberty stations, says it also supplies gas to many name-brand stations and all of its fuel contains detergent.
Mobil says its gasoline contains at least twice the amount of detergent as generic gas and that it adds the same amount to all three grades of gas.
Some name-brand stations may add extra detergent to their premium gas.
More than 90 percent of cars run fine on regular. If your owner's manual recommends regular, filling up with premium won't do a thing to help you. If your owner's manual says your car requires premium you should use it. If it's only recommended, you can experiment with regular and mid-grade and both should work fine.