Abstract: An improved flow distribution system for a catalytic reactor plenum chamber for a gas-liquid-solids ebullated bed reactor including a downwardly directed conduit and a flow distributor device such as a baffled nozzle attached to the inner end of the conduit, said nozzle containing at least two substantially parallel baffle plates usually oriented substantially normal to the nozzle inlet flow direction for providing initially downward flow and good mixing and radial flow disperson of gas-liquid materials in the lower portion of the plenum. The initially downward flow is then deflected generally upwardly by the curved lower head of the reactor plenum chamber and passes uniformly upwardly through a flow distribution grid into the ebullated catalyst bed. A sparger can be provided in the plenum above the flow distributor device for feeding additional gas-liquid mixture into the reactor.