Two sets of mature coals have been collected at outcrop on two dipping coal seams in the Ales Carboniferous coalfield (Massif Central, France). Visual examination, petrographic observations, and Rock-Eval pyrolysis studies unequivocally suggest that these coals have been weathered, the intensity of this alteration increasing progressively towards the soil. According to the reflectance (Rr) values of 1.7-1.8%, these coals have reached low volatile bituminous rank. In contrast to the reflectance, which does not exhibit any marked variation along the studied sections, T-max, although classically considered as a rank parameter, increases progressively with decreasing distance from the surface. This T-max increase is accompanied by a decrease in the hydrogen index (HI) and with an increase in oxygen index (01). All these changes are undoubtedly consequential to weathering. Thus in the present case, T-max must not be considered as a maturity indicator, but as an oxidation parameter like 01 and the O/C atomic ratio. This conclusion is also supported by the positive correlation between T-max and proportion of oxidised vitrinites (i.e. bearing oxidation marks) provided by maceral analysis. This peculiar behaviour of T-max in response to the weathering of mature coals is in total contrast with its invariance during low-mature coal alteration. This finding obliges us to moderate or even to revise the conclusions of a previous work on mature coals sampled at outcrop [Int. J. Coal Geol. 44 (2000) 49] where higher T-max than expected from Rr values, were supposed to have been necessarily caused by warm (and oxidizing) fluids. (C) 2002 Elsevier Science B.V. All rights reserved.