A conceptual design for the production of synthesis gas, suitable for methanol production, is presented. We propose the reforming of natural gas with high CO2 content by using H2O or H2O-O-2 as coreactants. A thermodynamic analysis for two reforming processes is developed to get adequate operating conditions for the reformer. The flow scheme for the syngas-methanol plant, together with the corresponding mass balances, is presented. A H-2 separation process is considered for syngas composition adjustment. The methanol-loop reactor was also included in the analysis to take into account its close relationship with the reformer's energy balance. For a comparative study, the hypothetical expansion of an existing methanol plant based on steam reforming of natural gas was chosen. A fundamental economic study shows that combined reforming (CO2 + H2O) and tri-reforming (CO2 + H2O + O-2) of CH4 are competitive processes, with lower operating and capital costs in comparison with steam reforming.