By comparing results generated from an advanced single-particle model with those obtained from experiment, we find reaction does occur within the boundary layer of a stationary char resident within the emulsion phase of a fluidized bed, with the extent of reaction diminishing as superficial gas velocity increases. Comparison also shows that the CO-O-2, C-O-2 and C-CO2 reactions all affect the particle related CO/CO2 product ratio, with the influence of each varying with temperature. These observations help explain the peculiar product ratio/temperature profile recently reported by Linjewile and Agarwal(1995, Fuel 74, 5) and suggest, for the first time, a relationship between the product ratio and char particle size. The model results show that boundary layer reaction influences the heat transfer coefficient associated with a char that is burning within a fluidized bed, and that any correlations which do not explicitly account for this may only serve as an approximation.