The numerical solutions for different formulations of the conservation equations based on the dependent variables. pressure (P), enthalpy (h), density (rho), entropy (s) and flow velocity (u) for highly transient flows are presented. The models are each in turn applied for simulating the transient fluid flow dynamics following the rupture of a real and a number of hypothetical pipelines containing liquid, flashing liquid, two-phase and a permanent gas. In the case of the flashing liquid and two-phase pipelines. a significant reduction in the computational run time for the Phu and Psu based simulations as compared to the conventional P rho u formulation is observed. The above effect is found to be much less pronounced for the liquid and permanent gas inventories. (c) 2006 Elsevier Ltd. All rights reserved.