Abstract The effective control of systems requires the formulation of suitably robust models of their behaviour. The work described in this paper describes the simulation and modelling of the behaviour of a bubbling fluidised bed. A simple system is investigated consisting of a vertical planar bed. The performance of the bed is characterised by measuring the proportion of the bed occupied by the voids associated with bubbles. From these measurements it is possible to evaluate the response of the bed to changes in the gas flow rate into it in the time domain and through transformation into the frequency domain. These techniques allow a simulation of the bed based on the work of Clift and Grace [R. Clift, J. Grace, Coalescence of bubbles in fluidised beds, A.I.Ch.E. Symp. Ser. 67 (116) (1970) 23–33.] to be validated. The simulation can then be used to evaluate a simple but effective physical model of a bubbling fluidised bed which treats it as being primarily a temporary store of gas. The model represents the dynamics of the bed well and in the form of a transfer function which can be used successfully as a basis for controlling the bed.