Abstract: A gas mixer and distributor has an array of parallel gas mixing and distributing tubes which extend from a first chamber through successive second and third chambers. Respective coaxial tubular sections surround the tubes and communicate between the second and third chambers. Openings in the walls of the tubes communicate from the third chamber into the tubes. The first gas is fed into the first chamber for distribution into the first ends of the tube. The second gas is fed into the second chamber and passes through the annular passages formed by tubular sections over the tubes into the third chamber. The annular passages provide indirect heat exchange between the first and second gases to produce uniform temperature and density of the second gas in the third chamber before passing into the tubes through the tube wall openings.