Oxidation behaviour of five high entropy alloys (HEAs): AlCoCrFeNi, Al2CoCrFeNi, Al2CoCr1.5FeNi, AlCoCrNi and AlCoCr0.5Ni, has been studied at 1100 °C in the cast-annealed condition. Al2CoCrFeNi and AlCoCr0.5Ni HEAs exhibit the lowest oxidation rates of the order of 10−12 g2 cm−4-s−1. Al-rich nanoscale precipitates are observed to aid protective oxide growth. The Al-lean phase fraction and its Al content also have a major effect on the alloy's oxidation behaviour. A parameter ‘X’ taking the ratio of these two has been introduced, which coupled with CALPHAD predictions can be a potential tool to shortlist HEAs for oxidation resistance applications. © 2021 Elsevier Ltd