The steady-state and impedance response of a solid metal point electrode in contact with a solid, oxygen-ion conducting electrolyte in CO-CO2 atmospheres was derived for three reaction mechanisms, involving gaseous species or species adsorbed on the surface of the electrode and/or the electrolyte. The overall electrochemical reaction was assumed to proceed in elementary steps, such as adsorption, diffusion of adsorbed species, and charge transfer. Eliciting the reaction mechanism from the steady-state response may require an extensive analysis in terms of temperature, gas-phase composition, and overpotential dependence. The impedance response, on the other hand, can in favorable cases be more distinctively dependent on the number of adsorbed species involved in the reaction and on the role of diffusion. Thus, if only one adsorbed intermediate species is involved, the impedance spectrum will always appear in the first quadrant of the impedance plane plot irrespective of experimental conditions. If two adsorbed intermediates are involved, however, this may lead to appearance of fourth-quadrant data.