The purpose of this paper is the co~rcelation of experimental results from three areas of pro~llant research: (0 low-temperature isothermal subliraation studies; (i0 the measurement of linear regression rates by the hot-plate pyrolysis technique; and (iiO the combustion of ammonium perchlorate (AP) at low ambient pressures, through either preheating the AP, the use of a solid volatile fuel, the passing of gaseous fuels through a porous bed of AP~ or the formation of a diffusion flame above the AP using a counterflow of fuel gases. Each of these experiments should yield information about the rate of sublimation of AP. Superficially, even when one allows for the accumulated experimental errors in the various types of measurements, the agreement between the results from the different techniques is not good. In particular, the activation energy for the rate-controlling step is in doubt, values of 20, 30 and 60 kcal/mole all having been suggested. R is shown that, when allowance is made for the pressure-dependence of the sublimation rate, then an acceptable degree of correlation between all the sublimation data is obtained and sablimation rates can be calculated from a simple kinetic theory formula with reasonable values of the evaporation coefficient.