The residual strains through the entire thickness of the zirconia layer of pristine and heat-treated thermal barrier coatings (TBCs) were mapped to help elucidate the failure mechanisms of TBCs. The strains were measured using 80.72 keV synchrotron radiation and a transmission geometry. The heat-treated TBC showed that a compressive strain formed in the zirconia layer of the TBC on cooling but this strain was diluted and reversed by the oxidation-driven expansion of the underlying metals. It also showed large (0.0024) out-of-plane tensile strains in the zirconia layer just above its interface with a thick underlying oxide layer.