Abstract: A portable liquid storage tank includes two elongate side walls, two end walls, a floor, and a roof, which are secured together to create a liquid-tight enclosure. The side walls are each preferably formed from a unitary piece of sheet material which is bent into three substantially planar sections which are angled at obtuse angles relative to adjacent sections. The tank thereby has a substantially octagonal shape. The floor is preferably sloped in a shallow V downward away from the side walls to assist drainage toward a drain. Each sidewall preferably includes at least one wedge-shaped brace located along the length of the sidewall and contoured to fit substantially flushly against the three planar sections of the sidewall. A plurality of support beams are secured transversely across the top of the side walls to provide additional structural stability for the roof. Several relatively large entryways are also provided in the tank and doors are provided thereto.