Chris Worling said he usually fills up his gas tank at a Shell or Chevron gas station, but definitely not at Costco because it generally costs 20 cents more.

"I tried the Circle K gas and it seemed to burn just as efficiently. But I don't know. It's just a name like anything else," Worling said.

Joe Velardi is a gas tanker driver and fills up tanks at a Costco, but he'll also stop at other different gas stations.

"I go to Shell, Tesoro, Chevron. I got customers from 7-Eleven to Costco to ConocoPhillips," Velardi said.

When he's finished, he'll motor back to the Shell Refinery in Martinez and got more gasoline for Costco.

Which begs the question: is there any difference between the gas at Costco and Shell, besides it costing 20 cents more per gallon?

The answer is yes -- and no.

"It's like medicine," Velardi said. "You've got your branded medicine and then your generic."

The difference is the branded cleaning additive each company puts in its gas to scrub fuel injector jets, or on older cars, the carburetors. It also helps the engine's valve seats.

Chevron, for example, calls their heavily advertised additive "Techron." The less expensive gas you would find at Costco or Circle K has the same sort of additive, but it's a generic.

University of California Berkeley's mechanical engineering professor Robert Dibble has spent a career studying motors and fuel.

"I have a Jeep Cherokee from 1993. It has 270,000 miles," Dibble said.

Dibble said he will vary the gas he puts in his tank.

"I buy gasoline, typically, at a lower cost station five times and then on the sixth time I will go to one of the name stations," Dibble said.

Insiders agree that consumers can easily protect their car with a simple additive from an auto supply store and it would be less expensive and consumers can pour it in their tank when they get an oil change.