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Coal permeability models are required to define the transient characteristics of permeability evolution in fractured coals during CBM recovery. A broad variety of models have evolved to represent the effects of sorption, swelling and effective stresses on the dynamic evolution of permeability. In this review, we classify the major models into two groups: permeability models under conditions of uniaxial strain and permeability models under conditions of variable stress. The performance of these models is evaluated against analytical solutions for the two extreme cases of either free shrinking/swelling or constant volume. For the case of free shrinking/swelling none of the swelling/shrinking strain contributes to the change in coal permeability because effective stresses do not change. Conversely, for the case of constant volume the full swelling/shrinking strain contributes to the change in coal permeability because the coal …