The interaction between finite-rate chemical effects and the nonsteady gas dynamics in the shocked gas, and its later effects on the characteristics of a detonation wave propagating in a 50% argon diluted hydrogen-oxygen mixture, is investigated. The in situ composition of the reactive mixture is obtained by utilizing the partial equilibrium hypothesis. In particular, the reactive flow field behind the lead shock of an experimentally measured marginal detonation is analyzed. The influence of the initial pressure and other variables is studied. The investigation shows that the lead shock decays faster in an ex, othermically reactive mixture than in a nonreactive gas. Increased initial pressures produce faster rates of lead shock decay and shorter induction periods. The extent of reaction in the flow behind a slowly decaying detonation wave is greater for the same magnitude of shock decay than that caused by a rapidly decaying detonation front. In the case of marginal detonations, the shock strength at the downstream end of the detonation cell is not adequate to cause spontaneous ignition of the gas, and the stability of the detonation is dependent on the transverse wave collision mechanism.