In 1944 ASTM Committee D-9 on Electrical Insulating Materials, under the sponsorship of Subcommittee IV on Liquid Insulation, instituted a field-testing program, the primary purpose of which was to evaluate the merits of two oil-sludging tests when applied to oils known to be of good, medium, and poor quality. The two tests, one the sludge accumulation and the other the pressure oxidation, represented at that time the latest development in accelerated oil-sludging tests. It was hoped that the two tests would fulfill a need long recognized by both producer and consumer of electrical insulating oil: that of distinguishing between the many brands of oil available, with respect to oxidation resistance and chemical breakdown during service. The well-known physical, electrical, and chemical screening tests, while generally used for purchase specifications, gave little indication of the oxidation resistance that could be expected of a given oil. Earlier sludging tests such as the Snyder Life test had proved to be inadequate, first because they were incapable, within a reasonable length of time, of distinguishing between oils of mediocre and excellent quality, and second, because it was not possible to establish a correlation between laboratory sludging time and expected life in service. In 1942 both the sludge accumulation and pressure oxidation tests were published as ASTM Tentative Methods D 670. Before advocating that the tests be advanced to standard status, Subcommittee IV desired to establish their adequacy not only for classifying oils for initial quality but also for predicting sludging propensity in service. It was for this reason that the 10-year field-testing program was initiated.