ABSTRACT Wet steam, being a two-phase fluid, has complex critical flow properties. Analytical and experimental data were used to investigate the critical steam flux, and the pressure ratio needed to achieve critical flow for a variety of popular flow-rate controlling devices. Three new parameters –– critical steam flux ratio, dimensionless critical steam flux, and the Napier parameter –– are introduced to correlate the critical flow data. Attention was focused on the effects of stagnation pressure, stagnation quality and design of the flow-rate control device on the critical flux. The study covered stagnation pressures from 200 to 2100 psia and stagnation qualities from 20 to 100%.