NOVELTY - Gas to liquids (GTL)-floating, production, storage and offloading (FPSO) system comprises: an FPSO facility (100) comprising a glassy oil separator (110) and an oil/gas separation unit (120); a reforming reactor (220); a liquid hydrocarbon producer; an upgrading reactor; a subsea carbon dioxide storage; and an internal power generator, where a hydrogen separator (230) and a carbon dioxide separation unit are provided between the reforming reactor and the liquid hydrocarbon producer and a water separator is provided between the liquid hydrocarbon producer and the upgrading reactor.    USE - The system is useful: in offshore oil fields; for producing synthetic fuel (claimed); in stranded gas fields.    ADVANTAGE - The system is easy to handle and transport, and is low cost.    DETAILED DESCRIPTION - Gas to liquids (GTL)-floating, production, storage and offloading (FPSO) system, comprises: an FPSO facility (100) comprising a glassy oil separator (110) and an oil/gas separation unit (120); a reforming reactor (220); a liquid hydrocarbon producer; an upgrading reactor; a subsea carbon dioxide storage; and an internal power generator, where a hydrogen separator (230) and a carbon dioxide separation unit are provided between the reforming reactor and the liquid hydrocarbon producer and a water separator is provided between the liquid hydrocarbon producer and the upgrading reactor, such that separated water and carbon dioxide, and water and carbon dioxide produced by the internal power generator are recycled to the reforming reactor and surplus carbon dioxide is stored in the used oil and/or gas fields. An INDEPENDENT CLAIM is included for method for producing synthetic fuel using the system, comprising separating crude oil and gas at FPSO facility and storing the separated crude oil in a crude oil storage, pretreating the separated gas by saturation and desulfurization, reforming the saturated and desulfurized gas with carbon dioxide and steam to produce a synthetic gas comprising carbon monoxide and hydrogen, providing the separation of hydrogen from the modified synthetic gas, providing the separation of hydrogen to an upgrading reactor and removing carbon dioxide from the remaining synthetic gas and returning the removed carbon dioxide to be used as a reaction source of the reforming, chemically reacting the hydrogen with carbon monoxide to produce liquid hydrocarbon, while separating water produced during the process and using the same as cooling water to remove reaction heat thus producing steam, where the steam is recycled to be used for the reforming, upgrading the liquid hydrocarbon with the hydrogen provided to the upgrading reactor; producing electric power by operating a fuel cell using the synthetic gas or hydrogen, with water and carbon dioxide being produced during the process, and producing steam using the water produced by the fuel cell as cooling water and returning the same to a reforming reactor along with the produced carbon dioxide.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a process for producing synthetic fuel using GTL-FPSO system.    FPSO facility (100)    Glassy oil separator (110)    Oil/gas separation unit (120)    Reforming reactor (220)    Hydrogen separator. (230)