Grease is oil with a thickening agent called a soap. The soaps may be based on most light metals such as lithium, aluminum, sodium, and calcium. The most "fibrous" of these is aluminum based grease, which is good for sliding applications. It is very water resistant but should never be used in rolling element bearings. The most common and versatile are greases based on lithium soaps. They feature excellent resistance to moisture and flowability for rolling element bearings. They handle heat well and resist thickening with age.

The best greases for most purposes are lithium based and contain molybenum disulphide. Molybdenum disulphide has the property of adhering to ferrous metals the extent that it requires machining to remove it. It continues to provide lubricity afte the grease is gone, as in washed away by solvent for a sort time.

Grease should be specified by NLGI grade, with or without the Moly additive.