What is re-refined motor oil used for ?

It's used essentially as a refined crude lubricant. Re-refined oil used to have a bad color associated with it because in the old days they didn't have modern technologies. They did some filtering and poured it over clay. They had these very, sort of, antique technologies. It did not make a high quality oil and it got a very bad reputation.

Today, with modern technologies, you could use it for passenger car motor oil, automatic transmission fluid, hydraulic fluid, heavy-duty motor oil. There's no difference between oils re-refined with modern technologies and refined oil from virgin crude.