The Gulf Stream system features some of the fastest and most persistent currents in the Atlantic Ocean and has long been identified as a promising target for renewable ocean current energy. This study investigates the theoretical energy potential of ocean currents for the Gulf Stream system. A simplified analytical model is calibrated and utilized to represent the quasi-geostrophic balance in the North Atlantic subtropical circulation. The effect of turbines is included in the model as additional turbine drag force. The energy equation in the system is derived and analyzed both locally and basin-wide. Basin-wide, energy production from surface wind stress is balanced by energy dissipation from natural friction and turbines. However, the pressure gradient is playing an important role in redistributing the energy in the local energy balance. It is found that increasing turbine drag does not necessarily increase total energy dissipation from turbines. The maximum energy dissipation by turbines is estimated to be approximately 44 GW, although electrical power output will be significantly reduced due to various engineering and technological constraints. The turbine drag has significant impact on the circulation system. The reduction of energy and volume fluxes in the circulation is featured for different levels of turbine drag. It is found that residual energy flux along the western boundary can be significantly reduced under the peak energy dissipation by turbines, while reduction of volume flux is less extreme.