Bituminous coals under mild oxidation conditions (55-95-degrees-C and oxygen pressure 100-1000 mbar) produce molecular dihydrogen in small but appreciable amounts. The source of the molecular hydrogen is the hydrogen within the coal macromolecule (C-H bonds) and not adsorbed water, as has been confirmed by labelling experiments. Hydrogen is produced in an oxygen-bearing atmosphere. The higher the temperature, the greater the amount of hydrogen produced. The phenomenon occurs with all the bituminous coals studied and is not dependent upon the particle size. The hydrogen concentrations produced are linearly related to the amount of oxygen consumed and only slightly dependent upon the amount of coal oxidized in a given reactor. This is the first detailed report on the evolution of molecular hydrogen at relatively low temperatures. Possible sources for the hydrogen produced as well as safety aspects of the handling of coal in confined spaces and mining are discussed.