As climate change worsens and temperatures rise, the ability to respond to novel environments becomes essential. Ectothermic animals are particularly vulnerable to environmental changes, as they rely on their surrounding environment to maintain their body temperature. Ectotherms at higher elevations often face interacting challenges, including temperature extremes, intense radiation, and hypoxia. To study the effect of oxygen availability on ectothermic thermal physiology and performance, we collected Pyrenean rock lizards (Iberolacerta bonnali) from high elevation habitats (2254 m above sea level). Lizards were split into two treatment groups: one group was maintained at a high elevation (2877 m ASL) and the other group was transplanted to a low elevation (432 m ASL). While the effects of hypoxia on thermal physiology are well-explored, few studies have examined the effects of hyperoxia. We predicted that lizards transplanted to low elevation would exhibit higher thermal preferences and voluntary thermal maxima, as the increased oxygen availability would aid in maintaining a higher metabolism. Additionally, we predicted that maximum sprint speed and the optimal temperature for sprint speed would increase in the transplanted lizards, corresponding with a shift in the shape of the thermal performance curve. These results give insight into mechanisms underlying the thermal physiology of this high-elevation specialist. They can be used to predict potential plasticity in the physiological and thermoregulatory responses to the novel environments created by climate change.