Particle concentration was an important factor that affected the gasification kinetics of carbonaceous material in gasifier. In this study, in situ gasification characteristics of particle swarm with different particle concentrations were investigated at high temperatures. The reaction rate of dispersed particle swarm was higher than that of dense particle swarm. Furthermore, it was demonstrated that molecular diffusion in high-temperature stage was the dominant diffusion mode. And the effect of particle concentration on diffusion process was limited. While the CO2 concentration in particle swarm evidently decreased with the increase of particle concentration. It was concluded that the CO2 concentration was the primary factor that affected the gasification of petcoke compared with the diffusion process in particle swarm at the same reaction temperature. The effects of CO2 concentration in particle swarms on intrinsic gasification kinetics of carbonaceous matter were generally underrated in present studies. (C) 2018 American Institute of Chemical Engineers