The spray characteristics of a shear coaxial injector at elevated pressures, using liquid and gaseous nitrogen to simulate liquid oxygen (LOX) and gaseous hydrogen, were examined under noncombusting conditions. Two injectors were evaluated with different LOX post designs, straight and tapered. Flow visualization tests have revealed a contraction of the spray with increasing chamber pressures below the critical pressure. At pressures above the critical point, stroboscope images revealed art elongation of the liquid breakup length. No differences in the spray morphology were evident for the two LOX post shapes. Droplet size and velocity measurements were made with a phase Doppler interferometric device for three oxidizer-to-fuel mixture ratios and a range of chamber pressures. The results indicated improved atomization at lower mixture ratios, but increased droplet sampling difficulty.