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IEC Publication 60599, concerning the interpretation of dissolved gas-in-oil analysis, was issued in 1999 by Working Group 13, as a result of the revision of IEC TC 10 of the previous IEC Publication 599, issued in 1978. The main body of Publication 60599 contains an in-depth description of the five main types of faults usually found in electrical equipment in service. The familiar gas ratios have been retained for the diagnoses, but with new code limits, while additional gas ratios are suggested for specific fault cases. More precise definitions of normal and alarm gas concentrations in service are indicated. In the Annexes, examples of typical (normal) gas concentration values observed in service are given for six different types of equipment. Extensive databases of faulty equipment inspected in service and of typical normal values related to various types and ages of equipment and types of faults have been used for the revision of Publication 60599. These databases are presented in this paper for the benefit of the maintenance personnel involved in the interpretation of DGA results in service.