Repeated breakdown of the protective oxide layer can be a key factor in the oxidation of zirconium alloys. Hence, accurate measurement of the oxide fracture strength is crucial for simulating the oxidation of these alloys. High resolution digital image correlation was applied to SEM images taken during in-situ tensile loading of oxidised ZIRLOTM. Bi-axial strain measurements obtained during crack formation in the oxide films were converted into stress, and fitted to Weibull distributions to predict the oxide failure strength. Analysis highlights the impact of surface roughness. Samples polished prior to oxidation gave a fracture strength of ∼1.6 GPa.