Estimates of Natural Gas Storage Capacity and Historical Maximum Storage Volumes, as of April 2009 and April 2010 (Billion cubic feet, unless otherwise noted)
	Demonstrated Peak Working Gas Capacity1		Working Gas Design Capacity2		Demonstrated Peak Working Gas Capacity as Percent of Working Gas Design Capacity (Percent)		Maximum End-of-Month Working Gas Inventories3
Region	Apr-2009	Apr-2010	Apr-2009	Apr-2010	Apr-2009	Apr-2010	Apr-2009	Apr-2010
East	2,178	2,196	2,268	2,281	96.0	96.3	2,032	2,097
Producing	1,202	1,297	1,351	1,383	89.0	93.8	1,068	1,224
West	509	556	694	699	73.3	79.6	470	524
Lower 48	3,889	4,049	4,313	4,364	90.2	92.9	3,565	3,833
Note: 1) 'Demonstrated Peak Working Gas Capacity' is the sum of the highest storage inventory level of working gas observed in each facility over the prior 5-year period as reported by the operator on the Form EIA-191M "Monthly Underground Gas Storage Report." The timing for peaks for different facilities need not coincide. 2) 'Working Gas Design Capacity' estimates a natural gas facility's working gas capacity, as reported by the operator on the Form EIA-191A "Annual Underground Gas Storage Report," and sums the result across all fields. It is a measure based on the physical characteristics of the reservoir, installed equipment, and operating procedures particular to the site that is often certified by Federal or State regulators. 3) 'Maximum End-of-Month Working Gas Inventories' is the maximum volume of gas reported in the Natural Gas Monthly by region or the lower 48. These data are the aggregation of gas in storage as reported by respondents on Form EIA-191M "Monthly Underground Gas Storage Report" for a given month. For the 5-year period ending April 2010, the maximum working gas in storage for the East region was reached in October 2009, the maximum working gas in storage for the Producing, West and Lower 48 was reached in November 2009. Information about storage regions is available at "Storage Basics." Sources: Form EIA-191M, "Monthly Natural Gas Underground Storage Report" and Form EIA-191A, "Annual Natural Gas Underground Storage Report."

The demonstrated peak working gas capacity for U.S. underground working natural gas storage for the lower 48 states as of April 2010 is estimated to be 4,049 billion cubic feet (Bcf), a 4.1 percent increase over last year's estimate. This estimate is based on demonstrated noncoincident peak working gas storage volumes for individual active gas storage facilities reported to EIA over a 60-month period ending in April 2010. Working gas design capacity, a less conservative indicator of natural gas storage capacity, also rose over the past year, increasing 51 Bcf, or 1.2 percent.

During the past year, the increase in natural gas storage capacity estimates can be attributed to the opening of new facilities, capacity expansion at existing facilities, and, for demonstrated peak capacity, greater use of existing storage facilities during the past year.

Demonstrated peak working natural gas capacity as a percent of working gas design capacity is lower in the West Region than the East and Producing Regions for several reasons. The West has several still-active fields whose primary role is not seasonal storage. These include fields used for pipeline load balancing and fields that are being drawn down to be taken out of service. Additionally, some fields in the West have large design capacities, but have infrastructure constraints that limit actual storage capacity.

Summary of Findings

Demonstrated peak working gas capacity increased 160 Bcf from April 2009 to April 2010, of which 95 Bcf was in the Producing Region and a 47 Bcf increase was in the West Region.

End-of-month working gas inventories reached all-time highs in the fall of 2009, with stocks for the lower 48 States at the end of November climbing to 3,833 Bcf. Starting in September 2009, working gas inventories exceeded the previously recorded high from October 2007, before reaching their all-time high in November.

There are several reasons for this:

Increased working gas design capacity: In November 2009, working gas design capacity was nearly 73 Bcf higher than the previous year, allowing for more available storage capacity.

Robust production coupled with declining demand: U.S. marketed production of natural gas in 2009 reached 21.9 trillion cubic feet (Tcf) — the highest recorded annual total since 1973. However, in 2009, total natural gas consumption declined roughly 2 percent from the previous year a reflection of 2009's mild temperatures and weak economic condition. This contributed to a higher than average volume of injections during the traditional injection season (from April 1 through October 31) — in 2009 net injections were 2,151 Bcf, nearly 150 Bcf greater than the 5-year (2004-2008) average.

High starting inventory levels: Inventories started off the injection season at 1,656 Bcf — significantly above the 2004-2008 average of 1,381 Bcf.

Favorable pricing environment for storage: Natural gas New York Mercantile Exchange (NYMEX) near-month futures prices were higher than spot prices for most of the year, providing storage operators incentives to put gas into storage to sell at a later date. Price differentials between the NYMEX near-month contract price and the Henry Hub spot price peaked in October and November of 2009, averaging 77 cents and 92 cents respectively.

Storage operators appear on pace to approach these all-time high levels for working gas in storage in the fall of 2010. According to EIA's Short-Term Energy Outlook (August 2010), the working gas inventory at the end of October 2010 is projected to be 3,752 Bcf, just 2.1 percent less than last year's record-high inventory.