My 300E calls for 91 Octane. If you are really concerned about saving money, you can fill up half and half with mid-range(89 Octance) and premium (93 octane) and you will be at exactly 91 octane. This isn't a real serious suggestion....you'll probably save $50.00 / year and is it really worth the hassle?? As Larry points out, your mileage will probably drop which reduces the savings. If you love your Benz, feed it the good stuff