Experiments were conducted to study the jet dynamics of unconfined and confined coaxial high-speed flows from radially lobed nozzles. The shear-layer growth rate of the lobed nozzles was found to be considerably higher than that of a conical nozzle. Pressure profiles indicated increased radial uniformity and transport of properties between flows. Increases in lobe height and number of lobes were associated with enhanced mixing and larger total pressure drops. The thrust loss observed was due primarily to divergent nozzle flow and duct friction losses. Use of a confining duct forced interaction of the flows and enhanced mixing. Compression of the primary flow produced intense compression-expansion regions in the flowfield. Another advance over earlier studies is the visualization of the axial vortices generated by lobed nozzles. These vortices can be linked to the observed cross-plane transport of properties.