An analysis is made of a model in which the heterogeneous reaction is 2C~,, + O. --' 2CO and the CO produced thereby undergoes the homogeneous reaction 2CO + 02 --* 2CO2; the homogeneous reaction interferes with the heterogeneous reaction through the consumption of O.. Constant density and unity Lewis number of the gas mixture are assumed. Self-similarity of the flow is also assumed, and the analysis is reduced to a problem of solving an ordinary differential equation for energy conservation. The effects of the surface Damkohler number Ds, the gasphase Damk6hler number D e, and the dimensionless surface temperature 7~,~ on the dimensionless combustion rate -f~ are investigated, When D~ = 0 or D e --' co, the solution can be obtained from degenerate governing equations; -f~ is independent of /~,. and simple relations hold between D, and -f.. The solution for D~ --* co exhibits singularity at the carbon surface. When neither D e = 0 nor D e --* co, the variations of -fw(DO, -f.(Ds), and -f.(~w) are determined numerically for the ranges of D~ (0.001 -100), D e ( 102_ 1014), and 7~. (0.15-0.40). It is found that (1) a sharp gas-phase reaction zone located away from the surface does not form, (2) -f~ increases with increasing D~ for any value of Dg and ~'w, (3) at a given D~, -f,. decreases with increasing D e for any value of/~.-how -f~, decreases with increasing log D e is roughly the same for all the values of 7~, (4) at a given D. -f. decreases with increasing 7~w for any value of De--how -f,~ decreases with increasing 7~w differs greatly with the value of D e.