Experiments simulating mixing of liquid oxygen (LO2) and liquid hydrogen (LH2) have been performed. The non-reactive mixtures were obtained by injecting jets of the oxidizer or simulant into a pool of the fuel or simulant. Three fluid combinations were tested : LO2 into liquid helium (LHe), liquid nitrogen (LN2) into LHe and LN2 into LH2. Experimental observations included flash X-ray and high speed video imaging, hot film anemometry, and thermocouple and diode thermometry. Results showed that the jet fluid stays coherent throughout the mixing process and that peak boiling of the pool fluid occurs shortly after jet impingement. Estimates of bulk density indicate a smaller range of variation than is currently being used for explosive yield calculations.