An experimental study was conducted to examine the effect of annular counterflow on the mixing of high-speed subsonic jets and slightly underexpanded supersonic jets. Suction was applied to a collar placed concentrically about a converging nozzle to create a counterflowing stream around the jet periphery. The primary jet was operated at exit Mach numbers between 0.4 and 1.2, for stagnation temperatures from 20 to 400°C. The results show that moderate levels of counterflow can be used to enhance the mixing between the jet and surrounding fluid. Furthermore, the counterflow control technique becomes more effective as the jet temperature is increased.