The oxy-fuel co-combustion behavior of two different herbaceous biomass species (beetroot and switchgrass) with bituminous coal was investigated by thermal gravimetric analysis (40 degrees C/min). The effects of sample kinds, oxygen concentrations and blend ratios on the co-combustion characteristics were obtained. The results showed that the incorporation of the beetroot or switchgrass could improve the combustion characteristics of the bituminous coal. The ignition temperatures (T-i) of the blends were very close to the pure beetroot and switchgrass. The T-i values of the pure beetroot and beetroot/coal blends were lower than those of the pure switchgrass and switchgrass/coal blends. The T-i values and T-b values of blends and their parent samples decreased with increasing the oxygen concentration. The comprehensive performance indices of blends and their parent samples increased with increasing the oxygen concentration. A significant interaction was detected between the bituminous coal and the beetroot or switchgrass during the oxy-fuel co-combustion. (C) 2013 Elsevier B.V. All rights reserved.