Carbon dioxide sequestration in aquifers is seen as a potential climate change mitigation technique. One physical mechanism by which this could occur is capillary trapping of discrete pore-scale CO2 bubbles (referred to as ganglia) in the pore space. Nuclear magnetic resonance (NMR) techniques were used to quantify the spatial distribution and pore environment of such CO2 entrapment in a model porous medium (random glass bead packing). 3D images revealed a relatively macroscopically homogeneous CO2 entrapment, even though the image resolution is insufficient to resolve individual CO2 ganglia. Quantification of the pore environment of the CO2 ganglia was achieved using NMR displacement propagators (displacement probability distributions), acquired both before and after CO2 entrapment. Lattice Boltzmann (LB) simulations were used to facilitate interpretation of the propagator statistics by considering various pore environments in which CO2 could become trapped. Comparison with the experimental data suggests that CO2 is preferentially entrapped in comparatively larger pores. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 1700-1709, 2011