Used motor oil is treated to remove contaminants, such as dirt, fuel, and water and distilled to separate light and heavy oils. Three products are made, asphalt flux (roofing materials), gas oil (refinery fuel) and base oil. The base oil is sold to blenders, who combine the base oils with additives to make finished lubricants like motor oil, transmission fluid and grease. Re-refined oil is the finished blend of base oils with additives and may be 100% re-refined content or blended with virgin base oil. Used oil can be re-refined over and over again, it never wears out - it just gets dirty.