Gas is so expensive these days, who wants to pay more for the premium grade stuff? But will filling your tank with the more expensive gas give you better mileage? Probably not. Any car that says premium fuel is recommended but not required will probably not get any better mileage with the expensive stuff. Your car might suffer a bit in the horsepower department... and I mean just a very little... but you will probably see no difference in your fuel economy. Modern engine technology can detect if you’ve pumped your tank full of regular or premium fuel, and it will adjust the spark plug timing... so as much as you hope that paying extra per gallon might save you big in the long run, it's just not so.  Although if you have a car that says it requires premium fuel, do not use the cheaper stuff just because I said so. You bought a luxury car that performs better on premium, so don't skimp on the gas if your owner's manual requires you to fill it with premium. For most cars, premium is not required... and will not help you get more MPGs if you spend the extra money to fill your tank with the premium grade.