In the present paper, the authors study the primary reactions of coal volatiles and a detailed mechanism has been made for three different environments: thermal decomposition (pyrolysis), partial oxidation (O2) and O2/CO2 gasification in a plug flow reactor to analyze the combustion component. The computed results have similar trend for three different environments with the experimental data. A systematically reduced mechanism for O2/CO2 gasification has also been derived by examination of Rate of Production (ROP) analysis from the detailed mechanism (255 species and 1095 reactions). The reduced mechanism shows similar result and has been validated by comparing the calculated concentrations of H2, CH4, H2O, CO, CO2 and polycyclic aromatic hydrocarbon (PAH) with those of the detailed mechanism in a wide range of operating conditions. The authors also predicted the concentration profiles of H2, CO, CO2 and PAH at high temperature and high pressure.