Models representing the pore structures of amorphous, mesoporous silica pellets have been constructed using magnetic resonance images of the materials. Using magnetic resonance imaging (MRI), maps of the macroscopic (similar to 0.01-1 mm) spatial distribution of porosity and pore size were obtained. The nature and key parameters of the physical mechanism for mercury retraction, during porosimetry experiments on the silica materials, were determined using integrated gas sorption experiments. Subsequent simulations of mercury porosimetry within the structural models derived from MRI have been used to successfully predict, a priori, the point of the onset of structural hysteresis and the final levels of mercury entrapment for the silicas. Hence, a firm understanding of the physical processes of mercury retraction and entrapment in these amorphous silica materials has been established.