The pressure-temperature explosion limits of H-2/CO/O-2 mixtures were analyzed computationally and theoretically. It is shown that, with the addition of even a minute quantity of H-2, the mixture explosion limits evolve from being monotonic to the non-monotonic Z-shaped response characteristic of H2O2 mixtures. It is further shown that the explosion limit at various conditions can be reproduced well with a reduced mechanism of 12 elementary steps and 10 species. Eigenvalue analysis of this mechanism leads to an analytic solution for the explosion limits, yielding explicit expressions for the degenerate high- and low-pressure explosion peninsulas as well as the individual first, second and third limits. The separate and coupled roles of H2 and CO oxidation are identified, leading to enhanced insight of this foundational component in the mechanisms of hydrocarbon oxidation, as well as useful information in the utilization of syngas. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.