A key to the success of long-term storage of CO2 in depleted oil or gas reservoirs is the hydraulic integrity of both the geological formations that bound it, and the wellbores that penetrate it. This paper provides a review of the geomechanical factors affecting the hydraulic integrity of the bounding seals for a depleted oil or gas reservoir slated for use as a CO2 injection zone. Potential leakage mechanisms reviewed include fault reactivation, induced shear failure of the caprock, out-of-zone hydraulic fracturing, and poorly sealed casing cements in enlarged, unstable boreholes. Parameters controlling these mechanisms include the upper and lower bounds of pressure and temperature experienced by the reservoir, the orientation and mechanical properties of existing faults, rock mechanical properties, in situ stresses, and reservoir depth and shape. Approaches to mitigate the likelihood of geomechanics-related leakage include the identification of safe upper limits on injection pressures, preferred injection well locations, review of historical records for reservoir pressures, temperatures and stimulation treatments, drilling program design to mitigate rock yielding in new wells, and assessment of wellbore integrity indicators in existing wells.