In this work, analysis of two-phase flow boiling instabilities in vertical and horizontal systems is presented. The steady-state system pressure-drop characteristics are determined by a numerical solution of the governing equations as derived from the Drift-Flux model. The transient characteristics of the two-phase flow are obtained for various parameters and the results are presented in graphical and tabular forms. The numerical solutions are determined using an explicit finite difference scheme. The results of numerical solutions are verified by the experimental findings. A satisfactory agreement between the theory and experiments is obtained. (C) 2009 Elsevier Ltd. All rights reserved.