There are currently three different classes of "Base stocks" to make engine oil.

1- Mineral based

2- Highly Refined Mineral oil

3- Synthetic based oils.

Mineral oils are formed through decomposition of a variety of organic matter such as fish, sea weed, trees, birds, grass, dinosaurs, etc.

Highly Refined Mineral Oils are just that. They are more refined which involves a variety of separation, hence a better Base oil to start from, but more costly to produce than petroleum.

Synthetic Base stocks in contrast to petrolium are built up from one or more specific organic compounds. They are well defined and are comprised of particular molecule types that have been designed for specific performance characteristics. One distinct advantage of synthetics is that they can be "tailor made" to fit the requirements of the application. There are currently 4 suitable synthetic base lubricants.

Polyalphaolefins(PAO's)

Synthetic Esters which include Dibasic Acid Esters (Diesters)

Polyol Esters

Polyalkylene Glycols (PAGs). The most common is the Polyalphaolefins(PAO's) .

Of course each has their advantages and disadvantages. There are also varying levels of quality in "Base Stocks". This is why the Amsoil Company uses a combination of "Synthetic Base stocks", as well as the highest quality to get the very best there is to offer! It is more costly, but in the long run, it becomes less expensive, as the oil provides excellent lubricity, improved energy efficiency, high viscosity index, low pour points (as low as -72 F.) excellent thermal and oxidative stability, high flash and fire points, and is fire resistant. And will last longer in use.(longer oil drain intervals of up to 35,000 or one year, which ever comes first)

How are Synthetic Motor Oils Made?

Have you ever wondered why synthetic oil is more expensive than petroleum oil and if it's worth it? The reason it is more expensive is because of how it is made. The name synthetic means that it is chemically synthesized from different hydrocarbons. They start with a hydrocarbon, then derive gas ethylene, and then chemically synthesize that into the base stock for synthetic polyalphaolefin or PAO.

Premium additives also add to the cost and are beneficial for reducing friction, resisting oxidation and thermal breakdown, and eliminating sludge and varnish formation.

There are 5 levels of additive packages the oil Companies can choose from. The Amsoil Company uses the highest level they can purchase.

So what does all that mean to you? Because the oil is synthesized from the same molecule, the molecules of the base stock of synthetic oil are of all the same size and there is no impurity. This causes the synthetic oil to be more stable, and will enable it do a better job of lubrication. So when you heat the synthetic oil it is less volatile. And when it gets -30 F., the oil will pour while the petroleum oil is solid. Also, over extended use the synthetic oil will retain its same lubricating quality longer.

In contrast petroleum oil's molecules are of different sizes and shapes, and some of the molecules are undesirable. Refining will remove most but not all of the impurities. The oil's viscosity and lubricating quality will change overtime because the smaller molecules will burn off, causing acids and sludge to form in the oil.