An infrared analytical method for isolating and identifying the major constituents in lubricating greases is outlined in this Bulletin. The basis of the method is a separation of the thickening agent, normally a soap, from the lubricating material normally an oil, based on their relative solubility in methyl isobutyl ketone. Infrared spectra of the relatively pure components are subject to appreciably easier identifications compared to the mixture. Additional chemistry and physical separations are possible after the initial separation which lead to further clean fractions for the performance of the infrared spectroscopic characterization.