Definitions

Design capacity: Design capacity, sometimes referred to as nameplate capacity, is based on the physical characteristics of the reservoir, installed equipment, and operating procedures on the site, which often must be certified by federal or state regulators. We calculate total design capacity as the sum of the reported working natural gas capacities of the 375 active storage fields in the Lower 48 states as reported on Form EIA-191, Monthly Underground Natural Gas Storage Report, as of November 2025. This total excludes 28 inactive fields in the Lower 48 states. The design capacity metric is a theoretical limit on the total amount of natural gas that can be stored underground and withdrawn for use.

Demonstrated peak capacity: Demonstrated peak capacity, or total demonstrated maximum working natural gas capacity, represents the sum of the largest volume of working natural gas reported for each individual storage field during the most recent five-year period, regardless of when the individual peaks occurred. This report considers demonstrated peaks from December 2020 through November 2025. Demonstrated peak capacity is based on survey data from Form EIA-191, Monthly Underground Natural Gas Storage Report, and is typically less than design capacity because it relates to actual facility usage rather than potential use based on the design of the facility. Significant temperature departures from normal for extended periods can influence use of natural gas storage capacity, which in turn, can affect regional or Lower 48 states’ estimates of demonstrated peak capacity.