AbstractComparative studies were performed to assess the biodegradation of the synthetic lubricant base stock, Priolube 3999, by P. putida using the CEC test method and manometric respirometry. Supplementary analyses demonstrated the production of a non‐readily biodegradable metabolite, trimethylol‐propane, the alcohol group of the candidate fluid. Evidence was obtained that indicated that a significant fraction of carbon added as test substance remained incorporated in the biomass. The implications of these results are discussed and modifications to the CEC test propo