Dense large-grain ceramic samples of Ba,YCu,O, have been oxidized at 400" to 500°C in 10 to 30 MPa of oxygen for I to 10 d . The high-pressure treatment has increased the equilibrium content x slightly above 7 but there is no concomitant increase in T,. At x=7.03 the superconducting transition, measured by ac susceptibility, has an onset temperature of -91 K and AT-4 K and no change in lattice parameter is observed. High oxygen pressure increases the rate of oxidation. [