Grease is formed by adding solid thickener in liquid base oil to form semi-solid state grease. The thickener functions as a sponge that absorbs base oil, and constantly releases it to lubricate. Oil separation over time is a function of grease consistency.  Such as , an NLGI Grade 000 grease could be expected to exhibit pronounced oil separation from the day of its manufacture.

The oil separation can sometimes be found on the top of the grease in bulk pails or drums. It is usually insignificant when the separated oil quantity is compared with the mass of grease present.  Such oils can normally be safely stirred back into the bulk of the grease in the container.

Experience has shown that much of this time-related oil separation can be reduced if the surface of the grease is kept smooth during storage; i.e., don't leave "craters" in the grease. Scrape top surface after each dispensing of the grease.