26 CFR 48.4041-16: -16 Sales for export.

(a) General rule. In order for a sale to be exempt from tax under section 4041 as a sale for export, it is necessary that the liquid be (1) identified as having been sold by the retailer for export and (2) exported in due course. To establish exemption from tax in the case of a taxable article for export, it is necessary that the retailer maintain adequate records and have in his possession documentary evidence showing that the article was so sold.

(b) Proof of exportation. Exportation may be evidenced by any one of (1) a copy of the export bill of lading issued by the delivering carrier, (2) a certificate by the agent or representative of the export carrier showing actual exportation of the liquid, (3) a certificate of landing signed by a customs officer of the foreign country to which the liquid is exported, or (4) a statement of the foreign consignee showing receipt of the liquid.

(c) Shipment to possessions of the United States. The same provisions as relate to sales for export and proof of exportation will apply to sales for shipment to a possession of the United States, within the meaning of § 48.0-2.