Abstract : One-dimensional propagation of a strong shock wave in a medium with an exponentially varying density is studied numerically. Solutions using various formulations of the energy equation are compared with the self-similar analytic solution. It was found that only the conservative energy equation predicts the correct shock propagation; the temperature and pressure formulations, even with artificial viscosity are far less satisfactory. This result holds over a wide range of different spatial resolutions and for different finite-difference algorithms.