So, my son bought the 2000 BMW 328i- I am keeping it for him until he deals with the speeding tickets... anyway... I filled the tank with regular gas- according to the owner's manual, premium is recommended, but the motor will run on regular fuel, albeit with less horsepower and worse fuel economy. Should I keep running it on regular? Or put in premium at the next fill-up? My buddy, Larry the BMW Lover, said "You won't notice the power difference or mileage difference-- so save money, and use regular gas." What do you think? Regular? Or premium?