This paper presents an analysis of data obtained by strain-gage experimental stress analysis on drum heads and nozzle openings in drum shells. This analysis, while referred particularly to power boilers, is also applicable to other types of pressure vessels. The data obtained are reduced to dimensionless form so that they may be applied to drums of other size and thickness but geometrically similar, and to illustrate more clearly the action of the drum in resisting pressure. The relationship between operating-stress level and the life of the vessel in service is discussed with particular reference to a drum that has given over 40 years of satisfactory service with an operating-stress range over a considerable area of the vessel of approximately the ultimate strength of the material. The effect of prestress created in the vessel by overpressuring, such as applying the 1½-times working-pressure hydrostatic test, is discussed.