"Our organization has been offered the opportunity to purchase re-refined oil at a significant discount. Can you explain the re-refining process and whether re-refined oil is as good as virgin base oil?"

Re-refining is a process used to refurbish used oil and return it to a high-quality base oil. In the United States, approximately 40 percent of used oil is captured and recycled in some manner, while 60 percent is lost. Nearly 14 percent of the captured and recycled oil is re-refined.

An expression commonly used to explain the gradual process of oil contamination, additive depletion and viscosity increase (thickening) is that the oil is "breaking down" and may no longer be able to maintain its lubricating qualities. Even though the additive package has been depleted, much of the base oil is still in relatively good condition. The re-refining of used oils is a process of repeating some or all of the five basic refinery processes to return the base oil to a usable condition or state.

Re-refiners use various processes to remove contaminants, water, spent additives and any of the original remaining additives from the used oil. The result is the reclamation of approximately 75 to 80 percent of the original base stock. A further process of refining and blending is then carried out to produce finished products.

Some re-refined oil is proving to be as good as, if not better than, virgin base oil. It is very dependent upon the re-refining technology and the source of the used oil. Independent testing by some laboratories indicates that "the performance and quality of re-refined oil is sometimes better than some virgin base oil stocks."

After testing some re-refined base oil, a report stated: "In summary, the oil is judged to be cleaner and lighter in color than some virgin oils tested, and is judged satisfactory for blending into various finished oils."

Tests that evaluated re-refined engine oils during a test period of about 15 months and in which the test vehicles remained in the program using re-refined oils for their total life expectancy of 60,000 miles (100,000 kilometers) concluded "that the performance of both virgin and re-refined oils were satisfactory for the operating conditions encountered and could be considered substantially equivalent."

Keep in mind that used oils that have been "reclaimed," "reprocessed" or "recycled" are likely of inferior quality and may have only passed through a settling and/or filtering process.