Abstract The various existing garnet–orthopyroxene geobarometers calibrated based on the Al 2 O 3 or Cr 2 O 3 components in orthopyroxene buffered by coexisting garnet for mantle xenoliths, abbreviated as Al 2 O 3 -barometer and Cr 2 O 3 -barometer, respectively, have been extensively studied, to test their precision by applying them to phase equilibrium experimental data, and to evaluate their validity by applying them to natural pyrolites. The Cr 2 O 3 -barometers failed in reconstructing the experimental pressures due to imprecise description of activities of garnet and orthopyroxene end members. Several of the Al 2 O 3 -barometers showed perfect ability in reproducing the experimental pressures and successfully discerned the garnet-facies and garnet–spinel transition facies lherzolites as well as the graphite- or diamond-bearing mantle xenoliths. It is recommended that pressure and temperature estimation of mantle xenoliths may be best determined simultaneously by combining the garnet–orthopyroxene barometer and the two-pyroxene thermometer of Taylor (1998). Orthopyroxenes containing Al 2 O 3 contents of less than 0.37 wt.% should not be used in the pressure estimation in order to avoid significant P–T errors propagated from analytical errors.