What is oil Made of?
No matter what brand of oil you use, the bulk of the oil is comprised of a base stock, which can be petroleum (crude oil), synthetic, or a blend. Various chemicals are then added to the oil to provide anti-wear, anti-foam, corrosion protection, neutralization of acids, maintenance of viscosity, detergency, and dispersancy properties. These chemicals are called the additive package, and depending on the oil they can simply meet, or far exceed the requirements of the American Petroleum Institute (API).

Petroleum Based Oils
These engine oils are called conventional oils and use petroleum that has been refined from crude oil as their base stock. An additive package of chemicals is then added to the oil, giving it the proper active ingredients to protect and lubricate your engine. These oils perform well in most automotive applications, and are relatively inexpensive to manufacture because they use natural crude oil as a base stock. A drawback with conventional oils is the limited capacity of the base stock to lubricate critical components and carry particulates as the oil ages, and the breakdown of the oil's shear strength with heat and over time. For these reasons, oil changes should be performed more frequently when using conventional motor oil.

Synthetic Oils
Synthetic Engine oils are made from a base stock that is synthesized from relatively pure chemicals for specifically designed performance characteristics. While this does increase the cost of the base stock, thereby increasing the cost of the oil, the benefits can be great. Synthetic oils offer superior low temperature flow, getting to critical engine parts quickly on startup and especially during cold starts to prevent engine wear. Synthetics also generally respond better to additive packages and are engineered with a greater capacity to lubricate under extreme heat and pressure conditions, so they offer superior wear protection. Synthetics can reduce engine deposits, reduce oil consumption, improve fuel economy, and will definitely make cold-starts easier if you live in a cooler climate. Jet engines use synthetic oils exclusively, so there is definitely a proven advantage to synthetic oils. So if you don't mind spending a little more when it comes time for an oil change, using synthetic motor oil will protect and lubricate your engine better, with a longer service life than conventional oil, meaning fewer oil changes.

Synthetic Blends
Just like the name sounds, a synthetic blend or "semi-synthetic" engine oil is simply a mix of conventional and synthetic base stock. While this type of oil does offer many of the benefits of full-synthetic oils, it also has the drawbacks of conventional oils. We generally feel that the middle of the road price of synthetics equates to middle of the road performance, but if you feel your engine needs some of the benefits of synthetics without the cost of full-synthetic oil, a synthetic blend might be right for your engine.

Viscosity
The viscosity of engine oil is the oil's most important property, and the term viscosity refers to the oil's resistance to flow. Since the engine oil must be able to flow to engine parts when the engine is started in cold conditions, and must also remain viscous, or "thick", enough to lubricate the engine at high temperatures, a good property of engine oil is to have minimum viscosity change for a given temperature change. The Society of Automotive Engineers (SAE) Viscosity Grade is a system based on a variety of tests, resulting in 11 distinct SAE grades of motor oil.