Numerical simulations are performed to study the effect of back pressure disturbances on a shock train. The basic problem consists of a shock train within a constant-area channel with a = 2 inflow and a back pressure applied to the outlet. By subjecting the shock train to different fixed back pressures, it is shown that the shock train length varies linearly with back pressure, while the shock spacing is conserved. Through back pressure step forcing it is shown that the response of the shocks, after an initial lag, is largely determined by the magnitude of the step change. Step increases in back pressure cause upstream shock movements with higher shock pressures. The opposite response occurs with back pressure decreases. With sinusoidal back pressure forcing the shock train oscillates at the applied forcing frequency. The forcing