A volatiles release model has been developed to predict the location and quantity of coal volatiles that are released into a bubbling fluidized-bed combustor, using overbed, in-bed or underbed feed systems. This model not only considers time resolution of the simultaneous processes of coal devolatilization and coal particle movement after injection, but also takes account of the stochastic nature of this particle movement. Volatiles release is nonuniform, occurring throughout an industrial-scale bed, but only in restricted parts of a laboratory-scale bed. For the industrial-scale bed, 32% of volatiles are released directly into the freeboard while the particle is devolatilizing at the surface, whereas 24% are released there for the laboratory scale bed. The model predicts the formation of numerous discrete volatiles regions within the bed, in agreement with a new interpretation of experimental measurements from an in-bed oxygen probe. The model is shown to be consistent with other experimental in-bed measurements obtained during combustion of “simulated” volatiles.