This guide is applicable to the detection and location of acoustic emissions from partial discharges and other sources in oil immersed power transformers and reactors. Both electrical sources (partial discharge) and mechanical sources (such as loose clamping, bolts, or insulation parts) generate these emissions. There are descriptions of acoustic instrumentation, test procedures, and interpretation of results. When this guide is used with oil-immersed reactors, it must be understood that interpretation of signals may be different because of the construction of the reactor. Accuracy of location depends on the type of fault, configuration of tank, type of instrumentation, and experience.