Experimental results are reported of the self-deflagration of the solid oxidizers hydroxylammonium perchlorate and hydrazine nitroform. The burning rate-pressure relationships were measured and combustion temperatures were determined. Quenching diameters were also measured for these two oxidizers plus ammonium perchlorate. Two findings of significance have emerged: first, hydroxylammonium perchlorate exhibits a low-pressure deflagration limit of 146 atm, analogous to the 20 atm limit of ammonium perchlorate. This high value obtains in spite of aflame temperature for HAP that is 100° higher than that of AP; and in spite of the fact that at pressures at which HAP does burn, it burns two to three times more rapidly than AP. Comparison of results for several oxidizers suggests that AP should be regarded as exhibiting an unusually low low-pressure limit. The second item of importance is an hypothesis that ammonium perchlorate deflagration occurs by a cellular mechanism. A simplified analysis of the AP combustion process in such terms lends excellent support to this contention.