Deep water hydrocarbon transfer system

System of a hydrocarbon transfer buoy (2, 82) and a vessel (3, 95), the buoy having a length (H1, H2, H3) of at least 50 m and a length-to-width ratio of at least 10:1, and comprising a submerged buoyancy member (5, 6, 7, 85) having a length of at least 30 m and being situated at a depth of at least 10 m below water level, a support frame (10, 96) being connected to the top of the buoyancy member (5, 6, 7, 85) and projecting above water level, the support frame carrying a support deck (11, 91) and a mooring buoy connector (36, 99, 102) for attaching to a mooring arm connector (21, 100) of the vessel, which mooring arm connector (21, 100) is situated on an arm (4, 92) projecting outboard from the vessel's hull (8, 95), the buoy being anchored to the sea bed via anchor lines (23, 24, 83, 84) which extend at an angle to a vertical direction, at least one hydrocarbon riser (12, 13, 93, 94) being attached to the buoy, characterised in that the support frame (10, 96) is an open support frame, the buoyancy member being connected to the sea bed via at least one substantially vertical taut tendon (31, 32, 33, 86, 87), the riser (12, 13, 93, 94) having a length of at least 500 m, and comprising a steel riser part attached to the buoy, the riser extending up to the mooring buoy connector (36, 99, 102) and being closable by a valve (16, 17, 88), the riser at its end comprising a connecting member (50, 51, 115, 116, 117) for releasably attaching to a duct (55, 56, 126, 127, 128) on the mooring arm connector (21, 100).