In this paper the thermoeconomic analysis of gas turbine plants with fuel decarbonization and carbon dioxide sequestration is presented. The study focuses on the amine (MEA) decarbonization plant layout and design, also providing economic data about the total capital investment costs of the plant. The system is fuelled with methane that is chemically treated through a partial oxidation and a water-gas shift reactor. CO2 is captured from the resulting gas mixture, using an absorbing solution of water and MEA that is continuously recirculated through an absorption tower and a regeneration tower: the decarbonized fuel gas is afterwards burned in the gas turbine. The heat required by CO2 sequestration is mainly recovered from the gas turbine exhausts and partially from the fuel treatment section. The reduction in efficiency and the increase in energy production costs due to fuel amine decarbonization is evaluated and discussed for different gas turbine sizes and technologies (microturbine, small size regenerated, aeroderivative, heavy duty). The necessary level of carbon tax for a conventional plant without a fuel decarbonization section is calculated and a comparison with the carbon exergy tax procedure is carried out, showing the good agreement of the results.