At the extreme end of the loading rate spectrum are creep tests. Creep tests are long term mechanical experiments for evaluating time-dependent effects of load and deformation. Creep tests are performed at a constant stress, or a combination of constant stress and deformation, while measuring the corresponding changes in deformation and/or stress. Creep segments are often incorporated as additional stages in compaction tests. A common procedure is to hold confining pressure, axial stress and pore pressure constant (all servo-controlled) and monitor the deformation over time. Alternatively, a creep segment can maintain axial stress, pore pressure and radial strain constant. The latter procedure may best represent reservoir behavior, although the former method provides information which can be interpreted more conveniently. The time to maintain these boundary conditions is ascertained during the creep stage itself, from an assessment of the equilibration of the volumetric and/or axial strain (or stresses, if appropriate) in time.