The National Bureau of Standards (NBS) has been working on the development of test procedures for recycled petroleum oils since 1976. The first phase involved development and evaluation of tests for characterizing used oil recycled as burner fuel, and has been completed. The second phase, on re-refined motor oil, involves development of a set of test procedures capable of monitoring the quality, consistency, and additive response of re-refined lubricating oil basestocks.Test under investigation include physical property tests, chemical property tests, hydrocarbon type characterization methods, and bench scale performance tests primarily directed toward the measurement of additive response. Cooperative efforts include the ASTM/NBS Basestock Consistency Study (involving both re-refined and virgin lubricating oil basestocks), a study of engine deposits with the U. S. Army Fuel and Lubricants Research Laboratory, and micro-oxidation test research at Pennsylvania State University. This paper describes the current status of this program, and includes representative data obtained on re-refined oils.