(a) Cost of property The Commission may investigate and ascertain the actual legitimate cost of the property of every natural-gas company , the depreciation therein, and, when found necessary for rate-making purposes, other facts which bear on the determination of such cost or depreciation and the fair value of such property. (b) Inventory of property; statements of costs Every natural-gas company upon request shall file with the Commission an inventory of all or any part of its property and a statement of the original cost thereof, and shall keep the Commission informed regarding the cost of all additions, betterments, extensions, and new construction. (June 21, 1938, ch. 556, § 6, 52 Stat. 824 .) CFR Title Parts 18 1b , 1c , 2 , 3 , 141 , 152 , 154 , 157 , 161 , 201 , 225 , 250 , 260 , 270 , 271 , 273 , 274 , 275 , 281 , 284 , 286 , 340 , 358 , 375 , 381 , 382 , 385 , 390