The oxygen-containing gases released during coal pyrolysis comprise more than a half of the devolatilization products, especially the noncondensible species. The mechanisms of CO formation reactions remain problematic, particularly the identity of the functional group precursors for low-temperature CO. In this paper, pyrolysis experiments of superfine pulverized coal were carried out in the N-2 and CO2 atmosphere under non-isothermal conditions, applying a fixed-bed reactor. The CO formation mechanisms were investigated from a functional-group standpoint. The deconvolution method via numerical analysis was adopted to resolve the multi-component envelop profiles of CO evolution. Five constituent reaction complexes induced by different oxygenated groups and reactions are recognized, combining the X-ray photoelectron spectroscopy (XPS) analysis. In addition, the effects of coal type, particle size, pyrolysis atmosphere and heating rate on the CO evolution were analyzed. Finally, different CO formation mechanisms initiated from the primary decomposition of distinctive oxygenated functionalities, secondary pyrolysis reactions of tars, and gasification reactions of chars are summarized. (C) 2014 Elsevier Ltd. All rights reserved.