19 CFR §10.538

1. (a)A person claiming preferential treatment under the SFTA for a good may claim that a fungible good or material is originating either based on the physical segregation of each fungible good or material or by using an inventory management method. For purposes of this subpart, the term “inventory management method” means:
   1. (1)Averaging;
   2. (2)“Last-in, first-out;”
   3. (3)“First-in, first-out;” or
   4. (4)Any other method that is recognized in the Generally Accepted Accounting Principles of the Party in which the production is performed or otherwise accepted by that country.
2. (b)A person selecting an inventory management method under paragraph (a) of this section for particular fungible goods or materials must continue to use that method for those fungible goods or materials throughout the fiscal year of that person.