Inter-state sale: movement of goods or transfer of title during transit determines cross-state tax character. A sale or purchase is deemed to occur in the course of inter-State trade or commerce if it occasions movement of goods from one State to another or is effected by transfer of documents of title during such movement. Delivery to a carrier or bailee fixes the commencement and termination of movement for this purpose. Movement that starts and ends within the same State is not inter-State merely because goods pass through another State. Co-mingled fungible gas introduced in one State and taken out in another is deemed movement between States.