Abstract: In the subject partial oxidation process for the continuous production of gaseous mixtures comprising hydrogen and carbon monoxide separate streams of a free-oxygen-containing gas are simultaneously passed through the center conduit and through the outer annular passage of a double-annulus-type burner while a liquid hydrocarbonaceous feedstock, optionally in admixture with a temperature moderator, is simultaneously passed through the intermediate annular-passage. In one embodiment, a dispersion of petroleum oil in steam is passed through the intermediate annular passage of the burner at a velocity which is greater than the velocity of the two separate streams of oxygen which are passed respectively through the central conduit and through the outer annular-passage. Combustion efficiency may be thereby improved.