15 U.S.C. § 717e — Ascertainment of cost of property

(a) Cost of property. The Commission may investigate and determine the actual legitimate cost of the property of every natural-gas company and the depreciation of that property. When necessary for rate-making, the Commission may also investigate and determine other facts bearing on the determination of that cost or depreciation and the fair value of the property.

(b) Inventory of property; statements of costs. Every natural-gas company must, upon request, file with the Commission an inventory of all or part of its property and a statement of the original cost of that property. The company must also keep the Commission informed about the cost of all additions, betterments, extensions, and new construction.