Abstract: A reactor having a vertically extending vessel wall (2) is provided with a plurality of staggered elongated parallel tubes (8) adapted for being filled with catalyst material and substantially vertically extending between an upper tube plate (10) and a lower tube plate (9), means (12, 13) for circulating a heat transfer medium between the tube plates (9, 10) alongside the tube walls (8), inlet means (3, 17, 18) above the parallel tubes (8) for distributing fluid in the form of one or more sprays and gas over the plurality of tubes (8) and outlet means (4, 20) situated below the plurality of tubes (8) for removal of fluids from the reactor, wherein the plurality of staggered tubes (8) are arranged in rows such that the tubes of adjacent rows are staggered, and wherein upper tube plate (10) is provided with openings (15), having a lower part in which the tubes (8) are closely fitted and having a substantially concentric upper part diverging in upward direction, the upper ends of the adjacent openings having edg