A compressed gas storage tank (10) is fabricated to conform to the dimensions of a convenient and/or available space, such as under the floor of an automobile. The tank comprises a shell (11-16) having at least a portion (11,12,14,15) fabricated from a superplastically formable material. The superplastic material is bonded to internal structural support members (17,18) and the remaining portions (16) of the shell. Bonding may be achieved by known methods such as welding and/or diffusion bonding. The internal support members, which need not comprise superplastic material, are positioned internally to provide optimum resistance to gas pressure hoop stresses. In contrast to a thick-walled cylinder, the tank of the present invention may be formed into an irregular shape allowing the tank to fit, for example, under a large fraction of the floor of an automobile by conforming to the available space. The relatively low gas containment efficiency of such an irregular shape is reinforced by the strength and toughness of the shell material, the internal trusses, and stiffening beads or ribs (13) that together constrain the hoop stresses caused by the compressed gas.