Rates of hydrogen formation in the temperature range 600C to 800C are reported for three coals of widely different rank. Between 35 and 70 percent of the total hydrogen available at any one temperature disengages with first order kinetics, but the apparent activation energies calculated from the corresponding rate constants are low and vary, for the coals in question, from ca. 8 to 15 kcal/mole. Since rate control by C-H bond rupture or gaseous diffusion must be ruled out, it is concluded that the rate determining step is a function of lamellar mobility, i.e. that hydrogen forms in a bimolecular process which occurs whenever two contiguous carbon lamellae move into an appropriate configuration.