The Energy Information Administration (EIA) provides weekly reports with estimates of working gas volumes held in underground storage facilities at the national and regional levels.
The overall approach relies on weekly survey data from a sample of operators of underground storage facilities. This data is used to prepare regional and national estimates for all underground storage.
The goal of the weekly storage data program is to provide weekly estimates of the level of working gas in underground storage for the United States.
(EIA) Weekly Gas Storage Report: http://tonto.eia.doe.gov/oog/info/ngs/ngs.html