The effect of weathering (natural oxidation) on the technological properties of cokes obtained at three different scales (laboratory, pilot plant and semi-industrial), from two medium volatile bituminous coals stored at INCAR open stockyard for several months, has been studied in this work. The results show that the procedure developed at laboratory scale is useful for studying the evolution of coke quality because the trends of the main quality indexes (mechanical strength and reactivity to CO2) are in agreement with those of the cokes produced at larger scales. Furthermore, it was found that the total porosity and the micropores specific surface area of the cokes vary with the scale of carbonization, and that they increase as follows: semi-industrial < pilot plant << laboratory. All of which are related to the evolution of the mechanical strength and reactivity to the CO2. (c) 2004 Elsevier B.V. All rights reserved.