A portable liquid storage tank is a large heavy gauge steel tank that is commonly used for temporary onsite storage of water and other liquids. Typically used in large cleanup operations, they are often called frac tanks because of their prevalent use in hydraulic fracking within the oil and gas industry. Most frac tanks hold up to 21,000 gallons and mini fracs hold 9,000 gallons. The most common type of liquid storage tank is the v-bottom or flat bottom, but there are also tanks designed to assist in agitation and circulation, separate liquids, and hold acid.