The helium resources base of the United States was estimated by the Bureau of Mines to be 1,070 bcf as of January 1, 1985. These resources are divided into four categories in decreasing degree of assurance of their existence: (1) helium in storage and in proved natural gas reserves, 280 bcf, (2) helium in probable natural gas resources, estimated at 243 bcf. (3) Helium in possible natural gas resources, estimated to be 287 bcf, and (4) helium in speculative natural gas resources, which makes up the remaining 260 bcf. These helium resources are further divided into depleting, nondepleting, and stored classifications. The depleting resources are those associated with natural gas fields that are, or will be, produced for the natural gas they contain. Almost all of the helium in potential (probable, possible, and speculative) natural gas resources is included in this classification. These depleting resources are estimated to contain 900 bcf of the total helium resource base. Helium resources contained in nondepleting natural gas resources, those in shut-in, abandoned, or otherwise nonproducing natural gas fields, are estimated to total 133 bcf. There is 37 bcf of helium in storage in the federal govenment-owned Cliffside gas field near Amarillo, Texas.