During pyrolysis and gasification, the pore structure of the feed material will change, and these changes affect the reaction rates. In this study, the surface area and reactivity of petroleum coke char prepared at different pyrolysis pressures were studied. In addition, the surface area and pore size distribution of petroleum coke have been monitored during gasification at various pressures. The change in these properties has been related to reactivity to determine how the physical structure of the petroleum coke influences the gasification rate. The samples were characterized using nitrogen and carbon dioxide physisorption and X-ray diffraction, while the reactivity was measured in a thermogravimetric analysis unit at 1173 K and total pressures of CO2 between 0.1 and 2.1 MPa. The surface area of char, prepared at higher pressures, is slightly higher than that prepared at 0.1 MPa. The corresponding increase in reactivity with an increasing surface area suggested that the different reactivities of chars prepared at different pressures were a result of the effect of the pressure on the surface area. In contrast to the minor effect of the pyrolysis pressure on the char surface area, an increase in pressure during gasification significantly increased pore development and, hence, surface area. Normalization of the reaction rate by the surface area indicated that the effect of the pressure on the physical characteristics of the petcoke was the main but not sole factor in the change of the reaction rate with the gasification pressure.