The theory of "pore blocking" is often used, particularly in combination with percolation theory, to develop methods of analysis for gas sorption data for the structural characterization of porous media. However, the evidence for the existence of the pore-blocking effect is conflicting and equivocal. In the work described here mercury porosimetry experiments were integrated with gas sorption to detect the existence of pore blocking effects during the desorption of nitrogen from a mesoporous sol-gel silica material at 77 K.