I am writting this to express my frustration with some of the more expensive synthetic motor oils, Such as : Amsxxx, Shafxxx, Royxx Purxx. Synthetics are a definite improvement over convential oil but the amount that these oils are better that Mobil 1 is not worth the extra money in my opinion. Case in point: I have a 1990 Dodge with 260K mile on it. IT has had mobil1 since 1000 miles. I have nevr had it apart except for the valve cover, and it is still like new clean, No sludge. A compression test has shown that all cylinders are within 5% of factory specs. If I had run one of these higher priced synthetics, would I have better results. I think not. True MObil1 is a giant step over conventional oil, and is well worth the price difference. But the amount that these other higher priced synthetics are better than Mobil1, is in my opinion negligible, and not worth the price.