Thermodynamic analysis of biomass gasification with recycled CO2 was investigated in this work to determine optimum operation mode and CO2/C ratio. Gasification System Efficiency (GSE), which takes into account the energy demand in the system, and CO2 emission per syngas production (CO2/Sg) were calculated to evaluate the performance of the gasification system. Considering the production of syngas at a H-2/CO ratio of 1.5, it was revealed that indirect gasification using biomass as fuel is the most efficient and environmental-friendly operation mode. The recycled CO2 proves to increase syngas production. However, when considering the additional energy demand required for processing the CO2 recycle, it was demonstrated that there are only some ranges of operating conditions (high pressure and low temperature) which offer the benefit of the CO2 recycle. The optimum CO2/C was reported to be around 0.1-0.2 for pressurized and low temperature gasification. (C) 2013 Elsevier Ltd. All rights reserved.