An investigation has been made of the process of coke formation in reactions of residual oil conversion on oxide catalysts based on activated aluminium alloys containing active components In and Ga in a quantity of 2-20%. The coke yield is extremal in nature and depends on the content of active components in the catalyst. It was established by thermogravimetry that the oxidation of coke deposits after the cracking of residual oil proceeds in the same temperature range, whereas, after steam and water treatment of the coked catalyst, oxidation of the coke deposits occurs at higher temperatures with different temperature maxima, which indicates the heterogeneity of the coke deposits. It has been shown that, during the reaction, the phase composition of the catalyst changes considerably under the action of the reaction mixture.