Neutron activation analysts techniques have been used to measure quantitatively trace impurities in mineral oils and organic esters. These impurities include arsenic, bromine, chlorine, cobalt, copper, manganese, mercury, sodium, and sulfur. The effects of processing and refining on the concentrations of the trace constituents are demonstrated. The effects of the trace constituents on response of the overall fluid to oxidation inhibitors and lubricity additives are indicated.