Crack nucleation has been the subject of important contributions in the two last decades. Starting from the double criterion of Leguillon (2002), the present paper suggests that an energy criterion is sufficient for the prediction of the loading level that triggers nucleation as well as its geometrical characteristics. In view of application to saturated porous materials, the role of the pore fluid during nucleation is considered. In case of low fluid compressibility, the presence of the fluid delays the brittle failure usually associated with nucleation, as long as the fluid pressure remains above the saturation vapour pressure. The energy nucleation criterion is then applied to discuss the formation of breakouts around wellbores subjected to remote compressive stresses.