One of the mechanics said that the bad gasoline looks like it was about 60 percent water. A Shell spokesperson said this is an isolated case and it does involve one underground case at this one Gilroy location.
The station and pump are shut down and crews are working to fix the problem.
John Denzel's brand new Buick was only able to move with the help of a tow truck. Another customer, Molly Elazier, was also stranded.
"I filled up last night about 10:15, made it to the on-ramp for 101 and tried to accelerate and nothing. All of a sudden my car decelerated and died on the shoulder," said Elazier
At least a dozen cars were affected, and in many cases the fuel simply paralyzed the engine.
"The engine died and then I tried to start it and it doesn't run anymore," said customer Benjamin Rodriguez.
Shell brought in a company from Santa Rosa to investigate how the gas became contaminated with water, but on Monday morning there were few answers.
"I feel embarrassed about the problem but we don't know what's going on," said Shell station manager Julio Magana.
On Monday afternoon, Shell issued a statement saying it is working diligently with the independent operator as well as state agencies to determine the cause.
Many motorists are angry that the station didn't shut down immediately. People continued pumping the contaminated gas for more than an hour.
"They weren't going around telling people don't put fuel in. People around here, myself, I was telling people don't put gas in your cars, they're not going to run," said customer David Brownson.
Excel Auto Repair was busy Monday doing work that started at about $400.
"Flush out the fuel filters, fuel system and the tank. You have to drain the tank completely and put fresh fuel in it," said Dan Marquez from Excel Auto Repair.
Shell reassured at least one customer it will cover any necessary expenses.
"Certainly it is my expectation and Shell has promised that we'll get them towed and repaired and they will pick up the expenses," said Denzel.
If you bought bad gas (between 10:15 and 11:00 p.m.), you're asked to call Shell at 1-888-GO-SHELL (467-4355) or e-mail firstname.lastname@example.org