Abstract A research on the fate of active groups from three typical petroleum cokes (petcokes) during gasification in a drop tube furnace have been presented. The results showed that the relative reduction (R) index can be used to assess the gasification reactivity of petcoke. The decomposition of side chain reaction of dealkylation is easier to proceed. Petcoke with a relative ordered degree of char structure has an energy barrier resulting in the transformation from the ordered graphitic carbon structure to amorphous carbon structure occurred only after the temperature reaches 1200 °C. It is recommended to control the petcoke gasification temperature above 1200 °C. A high temperature is beneficial for the conversion of oxygen-containing functional groups to hydroxyl groups. Petcoke with high ash content promotes the decomposition of functional groups to form active radicals, which favors the formation of amorphous carbon and, consequently, more active sites resulting in the high gasification reactivity. The high temperature gasification can make the stable active radicals (aromatic hydrocarbons groups) to break up the thermal barrier and convert to active radicals (aliphatic hydrocarbons and side chains on aromatic structure, oxygen functional groups and hydroxyl groups). The active radicals react with oxygen adsorbed on the carbon surface to generate CO, H2, CH4, etc.