Underground Natural Gas Storage


In California, natural gas serves as an energy resource for several purposes including: electrical power generation, industrial use,  residential use, and commercial use. To maintain an adequate supply of natural gas to these markets, Underground Gas Storage (UGS) reservoirs store natural gas. The UGS program within the Geologic Energy Management Division (CalGEM) helps ensure that storage operations are conducted safely through robust regulation.

Depleted natural gas or oil fields function as gas storage reservoirs in California. Natural gas is injected into the storage reservoirs through gas storage wells and stored until withdrawn for use. There are 12 underground natural gas storage fields in the state.  

Natural Gas Plant
An underground gas storage facility in California

Underground gas storage regulations require that gas storage wells are constructed to ensure that there is no single point of failure and that injected gas is confined to the approved storage reservoir. Current UGS regulations mandate that underground gas storage operators create and maintain risk management and emergency response plans specific to each UGS project. 


Underground Gas Storage facilities are also regulated by the United States Department of Transportation, Pipeline and Hazardous Materials Safety Administration (PHMSA). CalGEM has entered a 60106 agreement with PHMSA to act as a state partner and inspect UGS facilities on behalf of PHMSA. Additional information about the PHMSA underground natural gas storage program can be found on PHMSA's webpage here

Enforcement letters sent by PHMSA, as a result of CalGEM inspections, can be found on PHMSA's stakeholder outreach webpage here

Regulation Updates

Senate Bill 463 (Stern, 2019) directs CalGEM to review and revise its UGS regulations to address the root causes identified for the Aliso Canyon 2015 well leak and to develop regulations implementing a new chemical inventory reporting requirement for UGS wells. CalGEM is collaborating with public health professionals and soliciting comments from the public to create a formal draft of the proposed regulations to submit for Administrative Procedures Act (APA) rulemaking through the Office of Administrative Law (OAL). ​​

Unannounced Random Onsite Well (UROW) Inspections

Pursuant to PRC section 3185, CalGEM is required to “perform unannounced random onsite well (UROW) inspections of some gas storage wells annually.”  Although unannounced inspections are not new, CalGEM updated and formalized its UROW process in July 2022. The report(s) linked below give an overview and findings of CalGEM’s UROW Inspection program each year. 

​​​UGS Descriptions

​Underground gas storage project

  • A project for the injection and withdrawal of natural gas into an underground reservoir for the purpose of storage. An underground gas storage project includes the reservoir used for storage, the confining strata, gas storage wells, observation wells, and any other wells approved for use in the project. An underground gas storage project also includes the wellheads and, to the extent that they are subject to regulation by the Division, attendant facilities, and other appurtenances.

Field capacity

  •  The total gas storage capacity, including base and working gas capacity, of an underground gas storage facility, in cubic feet.​

Underground Gas Storage Data

​CCST: Long-Term Viability of Underground Natural Gas Storage in California​

Aliso Canyon Storage Facility Updates

California Public Utilities Commission : Aliso Canyon​