A parametric analysis of two gasification processes (i.e., steam-air and steam-CO2) of rice straw feed-stock is performed using a thermodynamic model-based approach developed in Aspen plus. The possibility of one step H-2/CO ratio adjustment in a gasifier at thermal self-sufficient condition is observed. The effects of changes in the ratio of gasifying agent on the syngas yield, H-2/CO ratio, total energy consumption and cold gas efficiency of the system at different gasifying temperatures in the range of 500-1000 degrees C are investigated. The syngas yield of both gasification processes significantly increases at low temperature until it reaches a maximum value and is stable at temperatures higher than 700 degrees C. However, the steam-CO2 system offers higher syngas productivity and a lower H-2/CO ratio. The total energy consumption of the system is also investigated, and the steam-air system consumes less energy and the thermal self-sufficient conditions are revealed, whereas the steam-CO2 system shows the inverse effect. Based on the thermal self-sufficient condition for syngas production, the operating conditions offering the highest syngas yield of 42% of with Fischer-Tropsch specification can be obtained at a gasifying temperature of 700 degrees C and steam-and air-to-biomass ratios of 0.57 and 1.17, respectively. At these conditions, the cold gas efficiency of 38% is achieved. (C) 2015 Elsevier Ltd. All rights reserved.