An articulated fluid loading arm especially suited for transferring petroleum from a storage or loading terminal to a marine tanker, and for returning vapor from the tanker to the terminal, comprising a support boom pivotally mounted on the deck of the terminal, a pair of fluid conduits extending along the boom from risers at the terminal, and a dual flow-passage drop-pipe assembly suspended from an outboard end of the boom. The drop-pipe assembly comprises a pair of upper conduit members, a pair of lower conduit members and a pair of intermediate conduit members pivotally interconnected by a plurality of knee joints and swivel joints into a pair of articulated diamond-shaped structures. One set of upper, intermediate and lower conduit members comprises an assembly for the transfer of fluid from the terminal to the tanker, and the other set of conduit members provides an assembly for the return of vapors from the tanker to the terminal. A support cable extends from a tanker connection means on the lower end of the drop-pipe assembly to the outboard end of the boom and then along the boom to a winch for lowering, raising and supporting the drop pipe assembly.