Asymptotic and computational methods are employed to investigate premixed laminar burning velocities of planar adiabatic flames in ideal gas mixtures containing carbon monoxide, oxygen, an inert, and trace amounts of hydrogen-containing species. The chemical-kinetic steps that control the burning velocity are identified, and the dependence of the burning velocity on composition, pressure, and temperature is determined. A lower limit to the burning velocity that is greater than 5 mm/s, independent of pressure, is established for totally dry stoichiometric mixtures at 300 K. The results contribute to understanding of CO flame structure.