Floating Production Storage and Offloading (FPSO) platforms are the most used floating structures in the offshore oil and gas industry. They are generally kept in place with the aid of mooring lines anchored to the seabed. In deep waters, the responses of mooring lines become more significant and difficult to be accurately captured through experiments or numerical quasi-static models. Thus, this paper assesses the influence of water depth, mooring line diameter as well as added inertia and drag coefficients on the behaviour of a deepwater turret-moored FPSO platform. The commercial software, AQWA, is used to conduct fully coupled time-domain dynamic analysis for the FPSO subjected to a unidirectional random wave. The results highlighted the influence of water depths and mooring line diameter in reducing surge motions and increasing mooring line tensions, at the same time furnishes valid information on the fluctuation trend of these responses. Drag and inertia coefficients were found to have little impact on the dynamic motions of FPSO. © 2019 Ain Shams University