Thermogravimetry (TG) and Fourier transform infra-red (FTIR) spectroscopy have been used to study the pyrolysis behavior and oxidative reactivity of molten caustic treated and untreated oil sand coke residues. In comparison with the Suncor delayed coke, the Syncrude fluid coke gave higher levels of CO/CO2 during pyrolysis while CH4 was only observed with the latter. However, the CO/CO2 evolution during pyrolysis of the caustic treated coke residues was determined to be similar and higher than the values obtained with the untreated fluid coke. This is attributed to the displacement of sulphur in the coke matrix by oxygen during molten caustic leaching. The oxidation reactivity of the coke residues was found to increase with caustic treatment. This increase is attributed to the increased surface area of the cokes.