We report new resistance and Hall effect measurements for Ba2YCu3O6+. The data were taken at temperatures up to 1100 K, and at various oxygen partial pressures. For T>700 K, the resistivity shows an activated temperature dependence, and a square-root pressure dependence. Measurements of oxygen content in the literature, however, show a dependence on pressure that is much weaker than square root. For the measurements of resistivity and oxygen content to be consistent, the mechanism for conduction at high temperatures is likely to be hopping. Our experiments are the first to show that the linear temperature dependence of the effective Hall carrier density persists up to 700 K and then drops. © 1988 The American Physical Society.