The method used by the Energy Information Administration (EIA) to compute U.S. maximum working gas in storage is different from that of its predecessor, the American Gas Association (AGA), and yields conflicting calculations, with the EIA’s estimate of full working gas levels much higher than AGA’s, the Department of Energy (DOE) agency said in a report this week..

For the AGA, the maximum amount of working gas was based on the sum of the largest volumes held in storage for each facility in a region at any given time during the survey period from 1992 through March 2000. Under this scenario, the historical maximum volume of working gas in storage in any given week could have been in excess of 3,294 Bcf had the AGA continued to carry out the weekly storage survey through the present, the EIA said. The AGA stopped conducting the survey last spring and turned it over to the EIA.

In determining the level of U.S. working gas capacity that was “full,” the AGA calculated the ratio of its estimated weekly storage volume to its historical maximum volume, the EIA noted.

In contrast, the EIA said it derives working gas estimates by subtracting base gas from total storage capacity. The EIA’s “recent data for total capacity and base gas are 8,376 Bcf and 4,355 Bcf, respectively, resulting in working gas capacity of 4,021 Bcf,” or about 727 Bcf higher than AGA’s calculation for maximum working gas during the eight-year reporting period.

As of Sept. 20, the agency estimated that 2,991 Bcf working gas was in storage. Using AGA’s approach, working gas capacity was 91% full, while the EIA calculates it as only 74% full.

“It is important to note that a given measure for percent full for the total U.S., regardless of computation method, may have limited usefulness in assessing the adequacy of inventories going into a heating season. This is true because more storage facilities are located near, and are designed for the most part, to serve local market areas. Storage facilities have, therefore, tended to cluster in a number of areas. Working gas stocks in the Producing Region can be directed to either of the other two regions [Consuming West and Consuming East regions], but sharing between the two Consuming regions is limited at best. Thus inventory status is more realistically assessed on a regional basis.”

For a more details of how the EIA calculates storage figures, go to www.eia.doe.gov under “What’s New.”

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