An analytical method is developed for predicting pressure variations in pressurized steam-surge tanks during liquid insurge. The steam in the tank is considered as a thermodynamic system. The effects on the steam of work done through compression, heat lost through the steam boundaries, and a spray of cold droplets into the steam region are taken into consideration. A solution to the equations employed was obtained by means of an iteration method. Performance curves have been determined with the use of an IBM 650 computer and results compared with those obtained experimentally for a pressurizer operating between 100 and 200 lb/in.2 (abs).