This paper presents a general overview of the methods used to refine conventional mineral insulating oils. The discussion will outline the individual refining processes and the effect each may have on the composition of the oil. Included will be a brief discussion of the Occupational Safety and Health Administration's Hazard Communication Standard, 29 CFR 1910.1200 as it can apply to mineral insulating oil and some suggestions for handling and storage of the oil to reduce contamination and degradation.