Cretaceous bituminous coals of known rank R¯0max, vitrinite reflectance) have been examined by ESR (electron spin resonance) and ENDOR (electron nuclear double resonance) techniques. Both highly oxidised (outcrop) and unoxidised mine‐run Balmer coal from the Crowsnest field have been subjected to heat treatment (200‐900°C), and the matrix proton ENDOR signal studied as a function of applied microwave and rf power. Changes in ENDOR line shape and intensity are described with particular emphasis on the presoftening region of the unoxidised coal. A comparative study of the carbonization of hvb and 1vb coking coal from the Crowsnest is reported.