I just bought a pontiac from a dealership and didn't ask what time of gas was in it
My car has 42000 miles.
My car has an automatic transmission.
After doing my research on your vehicle, I see that most people use regular gas(87) in their Pontiac Vibes. You should be getting around 22-27mpg. The better the gas you use the cleaner the gas will burn. I did read that some people with your type of car like to run 0% octane. Do I suggest this? No, not really. If I were you, I would simply use a can of sea foam every 3 or 4 tanks. This will keep your fuel system continuously clean and you wouldn’t have to worry about much. If you are using your car for performance reason i.e. racing you may want to use premium though.