As outlined in the foreword, Subcommittee IV on Liquid Insulation of ASTM Committee D-9 on Electrical Insulating Materials has held a series of seven symposia on insulating oils over a period extending from the fall of 1946 to the spring of 1957. The general theme of all these programs was derived from a very active interest of the subcommittee membership in the development of test methods and interpretation of test results for evaluating the serviceability of new and used insulating oils. It should be emphasized at the outset that all of the technical data and its interpretation together with any conclusions and opinions presented in any of the papers or discussions are independent expressions of the authors. In no case do these presentations necessarily conform with the concensus of Subcommittee IV nor imply sanction by formal action of ASTM Committee D-9. The first of the papers in the current program, by T. A. McConnell, is essentially an evaluation of laboratory test results with service performance of oils in selected transformers on the Detroit Edison system. The laboratory tests were made in conjunction with the extensive cooperative survey of Section B of Subcommittee IV recently completed This cooperative study was started about thirteen years ago with 19 different laboratories engaged in the testing of periodic oil samples from the transformers at about one-year intervals. The chief purpose of this survey was to determine the significance of sludge tests by ASTM Methods D 1313 and D 1314 in evaluating the resistance to oxidation of various types of new and used oils. Also it was the general practice of the 19 cooperating laboratories to make other selected tests commonly used as criteria of oil degradation, such as acid number, dielectric strength, color, interfacial tension, power factor, and resistivity. The correlation of the mass of laboratory data with the service performance in actual transformers proved to be a very extensive and perplexing task. The paper by Mr. McConnell goes far toward consummating this purpose in correlating the data from all the laboratories with service performance, and the cooperation of The Detroit Edison Co. was invaluable in this work.