An offshore unit equipped for crude storage and offloading to a shuttle tanker. Oil from a floating production unit is transferred by a flexible riser and a swivel through the turret. The main electrical power is also supplied through the turret from cables and slip-ring unit (the FSO is normally unmanned, with operation carried out by telemetry). Offloading from FSO to shuttle tanker is done through a flexible hose in the stern. When offloading operations are in progress, an azimuthing stern thruster ensures that the hull remains in the correct heading. The rise of the monohull floating production, storage and offloading unit with its onboard storage capacity has reduced the scope for separate FSOs.
An FSO stores and offloads hydrocarbons without hydrocarbon processing facilities.