Permeability may be altered in the Earth by plastic flow of the rock matrix. In order to better understand the relation between plastic flow and pore geometry, we measured the permeability of a suite of hot-pressed calcite samples with differing porosities. We found that the permeability dramatically decreased with decreasing porosity, particularly in the range of 10 to 4% total porosity. These results agree with a model for pore geometry changes during hot-pressing as previously developed for ceramics. Measurements of unconnected and interconnected porosity showed that the interconnected porosity virtually disappeared in samples with a total porosity of 4% or less. Scanning electron microscope observations showed that the porosity of samples above 10% total porosity were composed of large ‘spheroidal’ pores which were often connected by ‘tubular’ pores. During the last stage of hot-pressing, these ‘tubes’ are thought to collapse making the pore network disconnected.