The first determinations of critical stress intensity factors K//I//C and of fracture surface energy GAMMA of wet SiO//2 gels are presented. The examples comprise: (a) pure LUDOX gels, (b) LUDOX-AEROSIL composites, and (c) sonogels from alcoholates. K//I//C is shown to increase with the progress of syneresis but GAMMA stabilizes itself close to the surface energy of the solid phase exposed during fracture.