Systematic experiments were conducted to study the postflooding situation in air - water countercurrent flow in a tube of 0.025 in internal diameter with smooth inlet and outlet conditions for the two phases. The downflow rate of water and the pressure gradient were measured over a range of flow rates for test-section lengths of 0.6, 1.2 and 2.0 in. Additional experiments were conducted with increasing and decreasing water flow rates at a constant air flog, rate. The length of the test section or the way the flooding point was approached did not significantly affect the onset of flooding. The data show that, as the gas flow rate is increased, the pressure gradient can fall significantly in the postflooding situation due to depleting the downflow rate of liquid. Dimensionless correlations are proposed to calculate the downflow, rate and the pressure gradient given for overall flow parameters.