A compilation of the thallium isotopic data (along with previously published geochemical information) from organic-rich shales across the end-Permian mass extinction event, covering the latest Permian and earliest Triassic. Samples are from the Ubara and Gujo-Hachiman outcrops in Japan and Opal Creek outcrop in Alberta, Canada. The thallium isotopic analysis was done to constrain changes in global deoxygenation across the extinction event and link marine anoxia to the extinction. Analyses were done following thallium column chemistry and subsequent measurement on a Neptune inductively coupled plasma mass spectrometer. Modeling of the thallium isotopes was done using a forward geochemical box model in the Stella modeling program. This was used to determine the changes in extent of oxic seafloor necessary to induce the resultant compiled thallium isotope record from the aforementioned sections.