Sequestration of CO₂ into deep, unminable coal seams is an attractive option to reduce atmospheric emissions. However, coal seams commonly have low initial permeability, and CO₂ adsorption causes the coal matrix to swell, which further reduces the permeability and may result in inefficient injection_. We investigate numerically the impacts of coal swelling on coal permeability and, thus, CO₂ injection efficiency with constraints determined by experimental adsorption-associated volumetric strain measurements on three western Canadian coals. Our results show that injecting pure CO₂ markedly reduces permeability through time to the extent that it is not a feasible sequestration technology for almost all coals. However, injection of a gas mixture of N₂ and CO₂ (flue gas) markedly improved CO₂ injection efficiency while mildly reducing CO₂ sequestration capacity. The study also suggests that different geological settings and mechanical properties of specific coal seams strongly control coal seam permeability during gas injection and, thus, viability of CO₂ sequestration.