26 CFR 48.6416(h)-1: (h)-1 Accounting procedures for like articles.

(a) Identification of manufacturer. In applying section 6416 and the regulations thereunder, a person who has purchased like articles from various manufacturers may determine the particular manufacturer from whom that person purchased any one of those articles by a first-in-first-out (FIFO) method, by a last-in-first-out (LIFO) method, or by any other consistent method approved by the district director. For the first year for which a person makes a determination under this section, the person may adopt any one of the following methods without securing prior approval by the district director.

(1) FIFO method.

(2) LIFO method.

(3) Any method by which the actual manufacturer of the article is in fact identified.

Any other method of determining the manufacturer of a particular article must be approved by the district director before its adoption. After any method for identifying the manufacturer has been properly adopted, it may not be changed without first securing the consent of the district director.

(b) Determining amount of tax paid. In applying section 6416 and the regulations thereunder, if the identity of the manufacturer of any article has been determined by a person pursuant to a method prescribed in paragraph (a) of this section, that manufacturer of the article must determine the tax paid under chapter 32 with respect to that article consistently with the method used in identifying the manufacturer.