A gasification reactor comprising a vessel (1), provided at its upper end with a downwardly directed burner (2), and provided with supply conduits for an oxidizer gas (3), a carbonaceous feed (4) and a moderator gas (5), a combustion chamber (6) in the upper half of the vessel provided with a product gas outlet (7) at its bottom end and an opening for the outlet of the burner (2) at its top end, wherein between the wall of the combustion chamber (6) and the wall of the vessel (1) an annular space (9) is provided, and wherein the wall of the combustion chamber (6) comprises an arrangement of interconnected parallel arranged tubes (10) resulting in a substantially gas-tight wall running from a common lower arranged distributor (12) to a higher arranged common header (11), said distributor (12) provided with a cooling water supply conduit (14) and said header (11) provided with a steam discharge conduit (13) and wherein the steam discharge conduit (13) and the water supply conduit (14) are fluidly connected to a steam drum (29) and wherein the steam drum (29) is provided with a supply conduit (32) for fresh water and wherein the steam drum (29) is positioned at a higher elevation than the common header (11).