The vast majority of "full synthetic oils," in the marketplace are mostly comprised of hydrocracked petroleum oil (classified as a Class III Synthetic oil), but the base oil of Amsoil "100% Synthetic" lubricants are composed of a combination of a Class IV Synthetic oil (a true synthetic) derived from pure ethylene-gas to form PAOs (PolyAlphaOlefins) and a Class V Synthetic (another true synthetic) such as Alkylated Naphthalene or Esters, without a drop of petroleum.  The molecules of these Class IV & V Synthetics are of the same uniform shape allowing them to flow much more readily throughout the engines, transmissions and differentials, reducing damaging heat, creating more power and increasing fuel economy.  Also, the backbone of Amsoil 100% Synthetic lubricants have a much lesser tendency to attract oxygen molecules (where damaging oxygen can form sludge through the process of "oxidation").  By utilizing Amsoil "100% synthetic lubricants" within your vehicles, you will gain additional performance (where your engines become smoother, quieter and cooler), thereby increasing vehicles’ fuel economy (MPG), safely extending your oil drain capabilities, while greatly minimizing equipment breakdowns (all of which I had personally experienced).  If you view the many rave reviews on amsoil.com (Amsoil's Official Website) from "Verified Customers of Amsoil," who claim considerable MPG gains from using Amsoil products in comparison to other competitor's products, you'll be able to determine the mathematically-calculated savings per mile traveled in their vehicles (this may well entice you to test Amsoil Products for yourself, rather than my own experience with MPG gains). You will also see the various other wonderful benefits of Amsoil described by the Verified Customers of Amsoil (other than MPG gains) by clicking on the aforementioned link!