Abstract: Embodiments include methods and apparatus for mixing feedgases and producing synthesis gas. The apparatus includes a vessel containing a mixing system comprising one or more channels and a reaction zone downstream of the mixing system. A first feedgas and a second feedgas are separately injected into different injection portions of each channel, such that the second feedgas is injected in an acute direction into the first feedgas flowstream. The injected feedgases thereafter mix in a mixing portion of the channel. The mixing portion of each channel may have a reduced cross-sectional area so as to increase the total velocity of the feedgases while they mix. A feedgas mixture exits each channel of the mixing system to feed the reaction zone where it gets converted. Preferred embodiments include mixing O2 with a hydrocarbon gas and converting the mixture in a catalytic reaction zone to produce synthesis gas.