May 8 (Reuters) - U.S. underground working natural gas storage capacity in the Lower 48 states increased in 2024, the U.S. Energy Information Administration $(EIA)$ said in a report released late Wednesday.

The agency said it uses two metrics to assess working gas storage capacity - demonstrated peak capacity and working gas design capacity.

Working gas is the gas that is injected and withdrawn from the reservoir. It is in addition to the cushion or base gas, which is left in the reservoir to maintain adequate pressure.

Demonstrated peak capacity, which represents the sum of the largest volume of working gas reported for each storage field over a five-year period, rose 1.7% to 4,277 billion cubic feet (bcf) in 2024, according to the EIA.

Working gas design capacity, which represents a theoretical limit on the total amount of gas that can be stored underground and withdrawn for use, rose 0.1% to 4,671 bcf in 2024, EIA said.

EIA said demonstrated peak capacity increased for the second year in a row, noting that this year’s growth was due mostly to continued increasing utilization of gas storage facilities.

Another factor was a material change in California’s gas regulations to help ensure energy market reliability ahead of the winter of 2023–24.

In the aftermath of a massive gas leak from Southern California Gas' Aliso Canyon storage facility in 2015, California utility regulators limited the amount of gas that could be stored at Aliso Canyon.

EIA said those restrictions were eased somewhat in 2023, when the California Public Utilities Commission voted to increase the amount of gas that could be stored in Aliso Canyon.

Southern California Gas is a unit of California energy firm Sempra Energy SRE.N.

On design capacity, EIA said overall gas storage increased slightly in 2024 with additions in the Mountain region exceeding declines in the East and South Central regions.

(Reporting by Scott DiSavino; Editing by David Gregorio)

((scott.disavino@thomsonreuters.com; +1 332 219 1922; Reuters Messaging: scott.disavino.thomsonreuters.com@reuters.net))