The Schiehallion Floating Production Storage and Offloading (FPSO) is moored by a Turret Mooring System (TMS) located in 400m water depth in the Atlantic Frontier and submitted to very challenging environmental conditions. The Schiehallion FPSO went on stream in 1998. As part of the planned field development the QUAD 204 FPSO currently under construction will replace the producing unit in 2015. In both cases, SBM Offshore (SBMO) is the supplier of the Turret Mooring System. This paper compares the main features of Schiehallion and QUAD 204 TMS: mooring lines, connectors, weathervaning system, manifold and swivel stack arrangement. The performance of the key components over 15 years of operation is reported. The changes brought to the original design are highlighted and discussed.