An underground storage tank system (UST) is a tank and any underground piping connected to the tank that has at least 10 percent of its combined volume underground. The federal UST regulations apply only to UST systems storing either petroleum or certain hazardous substances.

Facilities with aboveground storage tanks (ASTs) holding oils of any kind may be subject to U.S. EPA's Spill Prevention, Control, and Countermeasure (SPCC) regulation (40 CFR Part 112). The SPCC regulation does not specifically use the term AST, but rather includes ASTs under the term bulk storage container. A bulk storage container is “any container used to store oil. These containers are used for purposes including, but not limited to, the storage of oil prior to use, while being used, or prior to further distribution in commerce. Oil-filled electrical, operating, or manufacturing equipment is not a bulk storage container.” Oil-filled equipment may also be subject to the SPCC regulation and should be included with the bulk storage container capacity when determining the facility’s overall aggregate oil storage capacity. Some ASTs may need to meet additional state or local regulatory requirements that safeguard human health and the environment from potential threats posed by ASTs. You should check with your state environmental agency for information on state and local requirements.