Detailed procedures for analyzing gas from gas spaces or gas-collecting devices as well as gas dissolved in oil are described for use in power transformers. The procedures cover: (1) the calibration and use of field instruments for detecting and estimating the amount of combustible gases present in gas blankets above oil, or in gas detector relays; (2) the use of fixed instruments for detecting an determining the quantity of combustible gases present in gas-blanketed equipment; (3) obtaining samples of gas and oil from the transformer for laboratory analysis; (4) laboratory methods for analyzing the gas blanket and the gases extracted from the oil; and (5) interpreting the results in terms of transformer serviceability. The intent is to provide the operator with positive and useful information concerning the serviceability of the equipment. An extensive bibliography on gas evolution, detection, and interpretation is included.<>