Hydrostatic pressure has been used as a tool in the study of creep in aluminun to show that there is a change of mechanism associated with the drop of activation energy for creep found as the temperature decreases below about 0.6Tm. Moreover, this change occurs, while the argument of the sinh (Ab&sgr;/kT) term in the usual lattice diffusion controlled theories of creep is still small with respect to one, i.e., before any sizeable vacancy supersaturation is build up.