An analytical model for the prediction of steam-water critical-flow pressure, mass discharge and pressure gradients in the approach region to critical flow is presented. The continuity, momentum and energy equations are applied to successive differential elements along the conduit and are solved numerically on an IBM-7094 digital computer for the maximum discharge flow rate. The proposed model assumes thermal equilibrium conditions and employs the modified Armand correlation to relate the void fraction to steam quality. The frictional losses in the momentum equation are obtained by two methods: a separated flow model and Armand model. A comparison of the analytical predictions with available test results on small diameter pipes shows that: 1) the present model agrees with the published test data; and 2) both frictional loss models are equally valid, and the selection of a particular method depends on the degree of conservatism desired.