Measurements of liquid oxygen (LOX) drop size and velocity in a unielement liquid-propellant rocket chamber are presented along with complementary measurements of drop size/velocity for simulants under cold flow conditions. The drop size comparisons between the cold flow and hot-fire conditions showed that the drops were larger for combusting conditions. This observation is argued to be consistent with effects due to differences in the flow fields between hot-fire and cold flow conditions and more rapid vaporization of smaller drops under combusting conditions. The use of the phase Doppler particle analyzer (PDPA) in obtaining temporally averaged probability density functions of drop size in a harsh rocket environment has been demonstrated. The PDPA measurements indicate that the atomization process is characterized by either the presence of nonspherical liquid structures or the production of extensive dense drop regions under these conditions. Finally, the need for more extensive studies under a wider variety of chamber conditions is indicated.