The invention relates to a mooring buoy (6), comprising a submerged part (13) and a part extending above water level (11). The part above water level comprising a fluid outlet duct (24) for attaching to a vessel (7), the buoy being anchored to the seabed via substantially taut anchor legs (27, 28). A substantially horizontally oriented fluid transfer duct (15) being attached to a connector (17) of the buoy in a non-rigid manner. The buoy comprises a substantially vertical fluid duct (21) between the connector (17) and the outlet duct (24) and a mooring connector (9) for attaching to a mooring line (8) of the vessel, wherein the length (L) of the buoy is between 20 m and 70 m and the ratio of the diameter (D) of the lower part (13) of the buoy and the length (L) being below 0.3, preferably below 0.2.