Abstract: An apparatus for offshore production of hydrocarbon fluids is disclosed. The apparatus comprises a base and a buoyant structure secured to said base and connected or adapted to be connected to a subsea well or wells. The key characteristics of the apparatus are that: (A) the apparatus includes storage facility means for fluid(s) received from the subsea well or wells and/or for processed fluid(s) produced by the apparatus; (B) the buoyant structure is tethered to the base by a plurality of flexible tethers; and (C) the buoyant structure comprises (i) a sub-surface housing containing facilities for processing fluids received from the subsea well or wells via said storage facility in said base; and (ii) a column extending upwardly from the housing to a level above the sea surface. The invention also relates to the buoyant structure per se.