This specification covers four grades of fuel oil made of used lubricating oils. These four grades of fuel are proposed for use in various types of fuel-oil-burning industrial equipment and commercial boilers under various climatic and operating conditions. The four grades of fuel oil covered in this specification are RFC4, RFC5L, RFC5H, and RFC6. The fuel oils shall contain a minimum volume of used lubricating oil-derived products as prescribed herein. The oils shall also be homogeneous consisting primarily of hydrocarbons. The fuel oil shall not contain excessive amounts of organic or inorganic acids, or both, and shall be free of solid or fibrous matter.