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 suggests future action. 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. May be applied only with caution to other liquid-solid insulating systems. In any case, the indications obtained should be viewed only as guidance and any resulting action should be undertaken only with proper engineering judgement. This consolidated version consists of the second edition (1999) and its amendment 1 (2007). Therefore, no need to order amendment in addition to this publication.