To increase syngas production and minimize soot, polycyclic aromatic hydrocarbon (PAH), and CO2 emissions resulting from biomass combustion, the evolution of biomass volatiles during O-2/CO2 gasification was simulated. A highly detailed soot formation reaction mechanism flowing through the reactor, involving 276 species, 2158 conventional gas phase reactions and 1635 surface phase reactions, was modeled as a plug flow reactor (PFR). The reaction temperature and pressure were varied in the range 1073-1873 K and 0.1-2 MPa. The effect of temperature on product concentration was more emphasized than that of pressure. The effect of O-2/CO2 input on product concentration was investigated. O-2 concentration was important in reducing PAHs at low temperature. Below 1473 K, an increase in the O-2 concentration decreased PAH and soot production. However, if the target of CO2 concentration was higher than 0.22 in mass fraction terms, temperatures above 1473 K reduced PAHs and increased CO. (C) 2012 Elsevier Ltd. All rights reserved.