Time- and position-resolved synchrotron small angle X-ray scattering data were acquired from samples of two Australian coal seams: Bulli seam (Bulli 4, R o =1.42%, Sydney Basin), which naturally contains CO 2 and Baralaba seam (R o =0.67%, Bowen Basin), a potential candidate for sequestering CO 2 . This experimental approach has provided unique, pore-size-specific insights into the kinetics of CO 2 sorption in the micro- and small mesopores (diameter 5 to 175 Å) and the density of the sorbed CO 2 at reservoir-like conditions of temperature and hydrostatic pressure.For both samples, at pressures above 5 bar, the density of CO 2 confined in pores was found to be uniform, with no densification in near-wall regions. In the Bulli 4 sample, CO 2 first flooded the slit pores between polyaromatic sheets. In the pore-size range analysed, the confined CO 2 density was close to that of the free CO 2 . The kinetics data are too noisy for reliable quantitative analysis, but qualitatively indicate faster kinetics in mineral-matter-rich regions.In the Baralaba sample, CO 2 preferentially invaded the smallest micropores and the confined CO 2 density was up to five times that of the free CO 2 . Faster CO 2 sorption kinetics was found to be correlated with higher mineral matter content but, the mineral-matter-rich regions had lower-density CO 2 confined in their pores. Remarkably, the kinetics was pore-size dependent, being faster for smaller pores.These results suggest that injection into the permeable section of an interbedded coal-clastic sequence could provide a viable combination of reasonable injectivity and high sorption capacity.