Some materials examined by mercury porosimetry are densified by the isostatic pressure. Expecially, very porous materials formed by aggregated particles undergoe a hierarchical pore collapse. Thus, an accurate data analysis requires the previous determination of the mechanism of pore collapse in order to account for. This work examines the complex and unusual behavior of gels when submitted to mercury porosimetry. The unusual behavior encountered complicates the mechanism identification and, therefore, the equation selection. However, the major part of the volume distribution as a function of the pore size can be determined with a good accuracy.