We have studied the influence of an electrostatic field on the process of methane adsorption on the surface of coal under various conditions. We have determined the values of the Langmuir adsorption constants for the coal samples and have analyzed the adsorption mechanism. We found that gas adsorption is intensified in an electric field. We established that one of the Langmuir constants for tectonically deformed coal is larger than for raw coal, while the other constant, which usually remains unchanged, tends to increase when exposed to the field. We estimated the surface free energy of the system and we established that it increases with an increase in the electric field intensity. According to the thermodynamics of spontaneous processes, usually the Gibbs free energy of a system tends to decrease as a result of intensification of adsorption, and therefore application of an electric field leads to its increase.