Lubricant physical properties are important in determining their suitability for the intended application and for comparing fluids. Some properties also provide insight into the remaining useful life of a fluid in service. In this chapter, we first review the components that go into making a lubricant. This is followed by a review of the most common ASTM International standard test methods used to measure a lubricant's physical properties. More information on the significance of tests for petroleum can be found in ASTM Manual 1, Significance of Tests for Petroleum Products, edited by Sal Rand [1].