A simple, three-parameter microcanonical theory of gas-surface reactivity is shown to predict experimental dissociative sticking probabilities for methane dissociative chemisorption on the Ni(100) surface over roughly ten orders of magnitude variation in both pressure and sticking-even at quantum state resolved levels of detail. Facile energy randomization within the transiently formed gas-surface collision complexes is postulated to make the pooled energy from 15 local degrees of freedom statistically available to surmount the barrier to dissociation. The apparent threshold energy for C-H bond cleavage of CH4 incident on Ni(100) is 67 kJ/mol, down from 432 kJ/mol in the gas phase. (C) 2003 American Institute of Physics.