Three different cokes obtained from the thermal cracking of Athabasca Oil Sands bitumen by delayed coker, fluid coker and flexicoker processes have been compared in terms of their chemical composition (elemental analysis) and physical structure (scanning electron microscope). Flexicoker coke has been found to have the highest metal values and lowest heteroatom content of the three cokes, and has a unique porous structure. These features favour the lability of the metals in this coke and may account for its previously noted susceptibility to chemical leaching.