This is probably a stupid question (I don't know a whole lot about cars lol) but does using premium octane give you better gas mileage? The dealership had my car filled with regular and I was only getting about 25 mpg. I filled it with plus on Saturday and I'm getting about 29 mpg now. My next tank is going to be premium so I can see the differences. I know that putting premium in will give the best performance for the car.