Abstract: A method of operating a three-phase slurry reactor includes feeding at a low level at least one gaseous reactant into a vertically extending slurry body of solid particles suspended in a suspension liquid, the slurry body being contained in a plurality of vertically extending horizontally spaced slurry channels inside a common reactor shell, the slurry channels being defined between vertically extending horizontally spaced divider walls or plates and each slurry channel having a height, width and breadth such that the height and breadth are much larger than the width. The gaseous reactant is allowed to react as it passes upwardly through the slurry body present in the slurry channels, thereby to form non-gaseous and/or gaseous product. Gaseous product and/or unreacted gaseous reactant is allowed to disengage from the slurry body in a head space above the slurry body.