Conventional petroleum oils are refined from crude oil, which is pumped from within the earth. The refining process, however, does not remove many of the impurities inherent in crude oil. These impurities detract from the lubricating ability of the oil and contribute to deposit, sludge, and varnish formation.

Synthetic motor oils are constructed in the laboratory and contain no impurities. Synthetic motor oils have uniform molecular structures and are designed for specific lubricating applications. The high temperatures or demanding operation conditions of modern engines do not affect them.