IEC 60599:2015 describes how the concentrations of dissolved gases or free gases may be interpreted to diagnose the condition of oil-filled electrical equipment in service and suggest future action. This standard is applicable to electrical equipment filled with mineral insulating oil and insulated with cellulosic paper or pressboard-based solid insulation. Information about specific types of equipment such as transformers (power, instrument, industrial, railways, distribution), reactors, bushings, switchgear and oil-filled cables is given only as an indication in the application notes. This standard may be applied, but only with caution, to other liquid-solid insulating systems. This third edition cancels and replaces the second edition published in 1999 and Amendment 1:2007. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) revision of 5.5, 6.1, 7, 8, 9, 10, A.2.6, A.3, A.7; b) addition of new sub-clause 4.3; c) expansion of the Bibliography; d) revision of Figure 1; e) addition of Figure B.4.