An experimental investigation has been made of the properties of high speed enclosed diffusion flames being fed by propane and air. The flames burnt within a rectangular chamber consisted of an array of 2, 3 and 4 air jets, the propane inlets lying in between. The study of the velocity profiles showed interesting results of the stability of the flow fields. Combustion can stabilize an air jet field. The blow off stability of such flames decreases with increasing number of air jets and depends on the width of the air slits. The recirculation velocities within the wakes are slightly higher with combustion than in cold flow. The length of the recirculation zone is independent of the air jet velocity and scarcely influenced by combustion. By using radioactive Kr 85 as tracer gas the path of the fuel and its mixing with the air jet could be followed. The turbulence fluctuations in these diffusion flames are of the same order of magnitude as in premixed flames. The results can qualitatively be explained with a model, by taking into consideration the recirculation flow and an initial flame located at the boundary of the air jet.