This paper aims at presenting a numerical study considering the effect of oxygen concentration varied from 21% (v/v) to 40% (v/v) in enriched-air-pine biomass gasification. The gasification technology still to be in the early stage of development in Portugal and numerical studies to describe potential scenarios of biomass usage (a large amount of pine residues are available) are needed. The study was carried out considering a thermodynamic dual stage model developed using the Matlab program. The concept of carbon boundary point (CBP) was used to study the effect of different operating conditions, namely, pressure, moisture, the steam-to-biomass ratio and the adiabatic versus allothermal condition at the optimum gasification point. From the numerical simulation, it was observed that the gasification temperature increases with the operating pressure for all experimented oxygen concentrations and decreases with the moisture content as a function of the oxygen content. The molar fraction of the hydrogen and carbon monoxide at the CBP decreases as a function of the oxygen content while that of the carbon dioxide and methane increases. Finally, it was concluded that both the energy and exergy efficiencies also increase with the oxygen content. (C) 2012 Elsevier B.V. All rights reserved.