This paper summarizes the results of an investigation of the critical-heat-flux condition for bulk boiling of water in uniformly heated round tubes where the inlet conditions were subcooled and exit pressures were below 100 psia. Choked flow was found to be prevalent under these conditions. The critical heat flux is shown to be a complex function of both local and inlet conditions. Detailed flow-pattern observations were made with an electrical probe. Many of the trends in the critical-heat-flux data can be related to the flow-pattern instability caused by slug flow.