NOVELTY - The method involves heating compacted biomass material within a reactor tube (14) to temperature at which organic molecules within the compacted biomass material break down to form dry ash and fuel gas mixture. The fuel gas mixture is withdrawn from the reactor tube. The ash is removed from the reactor tube through an exit. Ingress of air is inhibited into the reactor tube by compacting the biomass material at an entrance of the reactor tube to form a plug of the biomass material at the entrance and compacting the ash at the exit of the tube to form a plug of the ash at the exit.    USE - Method for producing synthesis gas from carbonaceous biomass materials i.e. organic lignocellulosic materials using a biomass gasifier system.    ADVANTAGE - The method enables obtaining direct diffusion rate to be even smaller by utilizing plugs at locations, thus efficiently producing the synthesis gas from the biomass materials, and yielding higher energy contents of 300 British thermal unit (BTU)/cubic feet. The process enables forming a barrier to the ingress of air into the tube, and plugging ends of the tube with biomass and ash serving to better contain the heat within the tube to promote gasification reaction, thus reducing risk of a fire in a hopper. The process enables a closing unit to be employed to minimize back-diffusion of the desired syngas product, and minimize heat loss to promote process efficiency and reduced hazard risks. The process enables porosity of the plugs to be adjusted by degree of compaction of the biomass material being transported, thus eliminating need for a lock hopper system to prevent the ingress of air into the tube or unwanted leakage of the syngas from an ash removal section by ensuring that the gasifier system operates with inlet and outlet pressures within limits.    DETAILED DESCRIPTION - The entrance is a throat (20). The exit is a manifold (32).    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of a biomass gasifier system incorporating neutral atmospheric pressure capability.    Biomass gasifier system (10)    Reactor tube (14)    Throat (20)    Manifold (32)    Closed-loop control system (40)