A partial oxidation burner and process for the manufacture of synthesis gas, reducing gas and other gas mixtures substantially comprising H.sub.2 and CO. A hydrocarbon, oxygen-rich gas and, optionally, H.sub.2 O or some other temperature moderator are introduced into the reaction zone of a synthesis gas generator in which, by partial oxidation at an autogenous temperature in the range of about 1700.degree. to 3500.degree.F. and a pressure in the range of about 1 to 250 atmospheres, said synthesis, fuel, or reducing gas is produced. For example, a hydrocarbon is introduced into the reaction zone by way of the inner assembly of a novel multitube burner, and a mixture of oxygen-rich gas and steam is passed through a coaxial conduit disposed about the outside of said inner assembly. Said inner assembly comprises a central conduit of circular cross-section, having a plurality of parallel open-ended tubes extending downstream from the exit end of said central conduit and in communication therewith. The tubes terminate in a surrounding nozzle, which is the exit end of the coaxial outer conduit.