Supercargo, a person who accompanies a cargo shipped to a foreign port, and is intrusted with the sale of it there, either as specially directed or to the best advantage, and with the investment of its proceeds in a proper cargo for the home or other market. As the supercargo's authority properly concerns the cargo, it is ordinarily dormant during the voyage, and is called into exercise by arrival at the foreign port; and though for the sake of the cargo and a market the supercargo may sometimes have the authority to determine the destination of the ship, yet he has none to interfere in the navigation of her, or in any respect to usurp the office and functions of the master. The powers and duties of a supercargo are not very specifically regulated by law or usage, but are determined in every instance by the express instructions of the shipper where such instructions are given, as they usually are. The supercargo is simply an agent, and is limited like other agents to the authority vested in him by his principal.

Yet, by construction of the law, new authority is conferred upon the supercargo by the existence and force of necessity; and it has been expressly held that if by any sudden emergency it becomes impossible for the supercargo to comply with the precise tenor of his instructions, or if a literal execution of them would defeat the objects of the shipper and amount to a sacrifice of his interests, it then becomes the duty of the supercargo to do the best he can for the shipper; and his acts done bona fide and with a reasonable discretion, in such an exigency, are binding upon the latter. A supercargo, like a master or foreign factor, generally buys and sells in his own name, and his acts in a foreign port, even after the death of the owner of the cargo, and while that event was unknown to him, are binding upon all parties.