Sustained oscillations have been experimentally observed when a surge tank is introduced up stream of a boiling channel. This dynamic state arises from an instability of the steady state of the system. These low-frequency oscillations are called pressure drop oscillations to distinguish them from the high-frequency density wave oscillations of boiling channels under constant pressure drop. The conditions under which these oscillations arise are that the steady-state operating point should be in the negative slope region of the boiling channel pressure drop characteristic and in the positive-slope region of the system pressure drop characteristic. The steady state should also be unique in the system pressure drop characteristic i.e. there should be no coexisting steady states. Under these conditions when this state is dynamically unstable the system shows sustained oscillations having a low-frequency. In this paper we discuss how the parameter values where these conditions are satisfied can be determined analytically and elegantly using results from the D-partition method and the singularity theory. The former allows us to determine regions in parameter space where an operating point is stable while the latter allows us to obtain different regions in parameter space where the bifurcation diagrams are qualitatively different. The superposition of results of these theories is used to determine parameter values where pressure drop oscillations occur. The predictions are verified with numerical simulations of the original nonlinear model for a horizontal channel. (C) 2000 Elsevier Science Ltd. All rights reserved.Sustained oscillations have been experimentally observed when a surge tank is introduced up stream of a boiling channel. This dynamic state arises from an instability of the steady state of the system. These low-frequency oscillations are called pressure drop oscillations to distinguish them from the high-frequency density wave oscillations of boiling channels under constant pressure drop. The conditions under which these oscillations arise are that the steady-state operating point should be in the negative slope region of the boiling channel pressure drop characteristic and in the positive-slope region of the system pressure drop characteristic. The steady state should also be unique in the system pressure drop characteristic i.e. there should be no coexisting steady states. Under these conditions when this state is dynamically unstable the system shows sustained oscillations having a low-frequency. In this paper we discuss how the parameter values where these condition are satisfied can be determined analytically and elegantly using results from the D-partition method and the singularity theory. The former allows us to determine region in parameter space where an operating point is stable while the latter allows us to obtain different region in parameter space where the bifurcation diagrams are qualitatively different. The superposition of results of these theories is used to determine parameter values where pressure drop oscillations occur. The predictions are verified with numerical simulations of the original nonlinear model for a horizontal channel.