Abstract: Filter apparatus for purifying oil contaminated water, comprising a pressure resistant container (1) having a cylindrical outer shell (2) and pressure resistant end walls (3A, 3B). Disposed within the container (1) are first (5) and second (15) cylindrical inner shells, arranged concentrically and extending between the end walls (3A, 3B) and defining an intermediate, annular filter chamber (23) enclosing a particulate, elastic, oil absorbing, regeneratable filter material (24). The end portions (13A, 21A; 13B, 21B) of said first and second inner shells are fluid impervious whereas the intermediate portions thereof (14, 22) are designed as screen tubes. An axially movable, annular transverse wall (26A, 26B) is disposed in each fluid impervious portion (27A, 27B) of said filter chamber (23), said transverse walls being movable towards each other for compressing the filter material under the influence of a pressure medium supplied to the annular chambers (27A, 27B).