Part of a continuing study of the complex problems found in the physics of reentry bodies. Zirconia is the eighth of a series of ablative materials investigated by mathematical techniques. This study reports the thermodynamic investigation of zirconia, Zr0, over a range of temperatures up to 6000 deg K and pressures up to 10 atmospheres. Two sets of equilibrium composition equations are used--one representing a pure gas phase, the other a heterogeneous system of gas and condensed zirconia. The gas phase of the heterogeneous chemical system, like the homogeneous gas phase, comprises five gascous zirconium-oxygen species. The results of the computational program are presented in both tabular and graphic form. The latter is a conventional Mollier diagram in which specific enthalpy is plotted against specific entropy, with cross plots of temperature, pressure, and modecular weight or moles of condensed zirconia.