Apparatus and method for degassing liquids particularly cationic monomers. Fluid comprising liquid to be degassed together with sweep gas is admitted tangentially into a column (10) and forced down the column by a tubular baffle (16) which defines, with the inner wall of the column, an annulus (18) that is closed at its top (20). After passing to the bottom of the annulus the fluid forms an even film over the inner surface of the column and gas disengaging from the liquid can rise up the column while liquid accumulates at the bottom of the column. To assist the disengagement of the gas from the liquid the column is preferably of increasing cross section towards the bottom so that the thickness of the film is also reduced.