Mixing rates of particles and gases in confined, coaxial jets are reported for tests with conditions simulating those of pulverized coal gasification and combustion processes. Gas velocity, particle mass flux, and gas composition were measured at various radial and axial locations downstream of the primary jet exit plane. Effects of inlet velocity, density, injection angle, particle loading level, and particle size on the rates of mixing were determined. Increasing injection angle and secondary velocity significantly increased gas and particle mixing rates, while effects of other variables were much less significant. Dispersion of particles lagged that of the gas in all cases investigated.