A new flooding correlation is developed by studying hyperbolicity breaking near a singular point in two-phase flow. Choking and instability correspond to zero and imaginary characteristics which occur when the hyperbolicity of two-phase flow is broken, respectively. Through comparison between results predicted by this model and the experimental data of tubes with and without blockage, it is shown that they are in good agreement with data. The role of the zero characteristics is investigated by comparing the presence model with the experimental data by Celata et al..