Experiments were performed using a shock tube in which both pure polymer and propellant specimens, mounted on the end wall, are suddenly exposed to a hot stagnant gas at about 1800 °K and 47 atm. The test gas consists of oxygen/nitrogen mixtures in which the oxygen mole fraction is varied from 0.18 to 1.00. The resultant ignition delay is observed to increase sharply as the mole fraction of oxygen is reduced and typical ignitability limits are 0.2 ˜ 0.3 mole fraction or 10 ˜ 15 atm oxygen partial pressure. Ignition delay time is found to be sensitive to total pressure as well as partial pressure. The effect of imbedded oxidizer is found to be significant when the ambient oxygen mole fraction is below 0.5 mole fraction. The theoretical ignition delay predictions of the gas phase and heterogeneous theories are shown to be too close for the experimental data to distinguish between them. A simple flat-surface stagnant exposure (a one-dimensional model) is found to be inadequate to resolve the question as to the dominant reaction in the ignition mechanism.