An apparatus for storage and/or transport of a pressurized fluid cargo, comprising: a multi-sided container adapted to hold the pressurized fluid cargo under pressure at a specified normal operating pressure that is at least 0.15 MPa greater than atmospheric pressure, the container having a pair of opposing heads (16a, 16b) and a wall section between the heads, the wall section defining a non-circular cross-section and comprising adjacent and substantially planar, flexible sides (12a, 12b, 12c, 12d) joined together by rounded corners (14a, 14b, 14c, 14d), wherein the sides have a wall thickness, wherein the container is sufficiently rigid to be self-supporting when empty, and wherein the container is adapted to allow the sides to expand outwardly by at least the amount of the wall thickness while the container contains the pressurized fluid cargo at the specified normal operating pressure; and an external support system to limit the outward deflection of the side walls of the container while the container contains the pressurized fluid cargo at the specified normal operating pressure, with no support being provided to the rounded corner of the container, thereby enabling centre-span deflection of the side walls without plastic deformation thereof; characterised in that the external support system comprises a frame comprising a plurality of support members, wherein a portion of the plurality of support members define a void space, in which the container is received. a multi-sided container adapted to hold the pressurized fluid cargo under pressure at a specified normal operating pressure that is at least 0.15 MPa greater than atmospheric pressure, the container having a pair of opposing heads (16a, 16b) and a wall section between the heads, the wall section defining a non-circular cross-section and comprising adjacent and substantially planar, flexible sides (12a, 12b, 12c, 12d) joined together by rounded corners (14a, 14b, 14c, 14d), wherein the sides have a wall thickness, wherein the container is sufficiently rigid to be self-supporting when empty, and wherein the container is adapted to allow the sides to expand outwardly by at least the amount of the wall thickness while the container contains the pressurized fluid cargo at the specified normal operating pressure; and the container having a pair of opposing heads (16a, 16b) and a wall section between the heads, the wall section defining a non-circular cross-section and comprising adjacent and substantially planar, flexible sides (12a, 12b, 12c, 12d) joined together by rounded corners (14a, 14b, 14c, 14d), wherein the sides have a wall thickness, wherein the container is sufficiently rigid to be self-supporting when empty, and wherein the container is adapted to allow the sides to expand outwardly by at least the amount of the wall thickness while the container contains the pressurized fluid cargo at the specified normal operating pressure; and an external support system to limit the outward deflection of the side walls of the container while the container contains the pressurized fluid cargo at the specified normal operating pressure, with no support being provided to the rounded corner of the container, thereby enabling centre-span deflection of the side walls without plastic deformation thereof; characterised in that the external support system comprises a frame comprising a plurality of support members, wherein a portion of the plurality of support members define a void space, in which the container is received.