A RETRAN model was developed for determining the stability of boiling water reactors. This model was benchmarked against plant data from stability tests conducted during plant operations. The stability analysis with RETRAN is demonstrated using best-estimate RETRAN input data representative of the nuclear steam supply system. All of the important neutronic and thermal-hydraulic feedback mechanisms are taken into account through the modeling of the reactor vessel, recirculation loops, and core neutronics. The analysis was performed with the RETRAN-02/MOD003 computer code. The transient is initialized by a small step decrease in the steam dome pressure. The core exit (upper plenum) pressure and core power transient responses to this perturbation are transformed into frequency data and a system transfer function is then obtained. The system transfer function is fitted to a second-order equation from which the decay ratio and natural frequency can be determined.