Abstract: A container for holding fluent material comprises a bag of flexible material defining a volume for containing a load of material, a rigid base for supporting the bag, and tension members within the bag for constraining the bag to assume a shape in which the bag is generally rectangular in horizontal cross section when a load is contained within the volume. The bag has four side walls, a top opening in communication with the volume for loading of fluent material into the container, and a bottom. The tension members include a first elongate flexible tension member extending across the interior of the bag between a first side wall and a second side wall of the bag, and a second elongate flexible tension member extending across the interior of the bag between a third side wall and a fourth side wall of the bag.