The apparatus includes a spar buoy comprised of an elongated column mounting a platform at its upper end, the platform carrying a helicopter pad and a movable boom for assisting the mooring of tankers to the buoy and off-loading oil to the tanker. The platform includes a ballast system providing an adjustable counterweight to the movement of the boom. The buoy is anchored and oil lines from production or control platforms or underwater oil storage tanks extend upwardly through the buoy to the boom for delivering oil to an awaiting tanker. The buoy has an anchoring collar located therealong in a manner to limit the tilt angle of the buoy within a predetermined angle and to limit the lateral excursion of the lower end of the buoy through which the oil receiving lines pass to within a specified range. The buoy is constructed to obtain a long natural period whereby the amplitude of vertical movement due to excitation forces caused by wave action is reduced.