CO2 gasification with different coals and a petroleum coke from China were performed in a thermogravimetric analyzer (TGA). Initial gasification rates of these sample chars were measured at different gasification temperatures (850-1300 degrees C) and four particle sizes (< 40, similar to 100, similar to 250, and similar to 500 mu m). An nth-order model was used to describe the gasification kinetics. It is found that the measured gasification rate decreases as the particle size increases for three coal chars. For PC char, the gasification rate of size about 250 pm at temperatures of 850-1000 degrees C is similar to that of < 40 mu m, whereas the gasification rate of size about 250 mu m is obviously different from that of size about 500 mu m. The sensitivity of gasification rates to particle sizes for these samples is quite different. The effectiveness factor and the Thiele modulus with an nth-order model were calculated in order to quantify the influence of the pore diffusion resistance on char gasification. The results show that for the char with higher gasification reactivity, the effect of particle size on the char gasification is more prominent and the pore diffusion resistance is stronger. Furthermore, comparisons between experimental effectiveness factors and calculated effectiveness factors were made to confirm the validity of the model used in this study. (C) 2014 Elsevier B.V. All rights reserved.