The paper deals with the relative values of those factors that impose the present practical limits to power-station efficiency.The processes involved in the generation of electricity from coal are discussed, and the relative heat-release values of steam at various temperatures and pressures are examined.A method of power-station-efficiency analysis is employed by which the values of the following factors can be separated out and compared:—(a) Steam and vacuum conditions.(b) Coincidence of plant-item efficiencies.(c) The regenerative feed-heating cycle.(d) The re-superheating cycle.The influence of the present physical limitations of the properties of metals is examined in relation to the choice between the use of higher steam temperatures and the use of the re-superheating cycle.A form of power-station-efficiency rating is discussed, with a view to expressing clearly the efficiency merit of a power station.General conclusions are drawn as to the probable lines of future development.