Several metals, Mo, Pb, and Pt, have been compressed in a diamond anvil cell to 272 GPa and studied by energy-dispersive x-ray diffraction using a synchrotron source. The bcc phase of Mo was found to be stable to 272 GPa at 300 K, and the phase transition reported in shock compression at 210 GPa and 4100 K was not observed. This implies either a large hysteresis and/or significant vibrational and electronic contributions to the entropy change at the transition. The measured static equation of state of Pb to 272 GPa employing Pt and Mo as pressure standards shows stiffening as compared with shock data, and the reasons for this difference are discussed. © 1990 The American Physical Society.