[en] Monolithic alpha-2 alloys are being considered for applications in gas turbine engines at temperature between 593 and 705C. The alpha-2 alloys have better creep and oxidation resistance than conventional Ti alloys in this temperature range, but concerns over low temperature mechanical properties, interstitial embrittlement and hot salt stress corrosion cracking have limited the application of these alloys. Protective coatings address environmental concerns, while improved processing and chemistry may improve mechanical properties. The compositions of alpha-2 alloys have evolved over time to obtain a better balance of properties. Two prospective alpha-2 compositions are Ti-25Al-10Nb-3V-1Mo and Ti-24.5Al-12.5Nb-1.5Mo. This work characterizes the isothermal oxidation behavior of these two alloys in the 593-705C temperature range and discusses observed differences. The isothermal oxidation behavior in air of Ti-24.5Al-12.5Nb-1.5Mo was superior to Ti-25Al-10Nb-3V-1Mo and T-6242 in the temperature range of 593-705C. The 12.5-1.5 alloy was better because an external alumina scale formed which grew more slowly than the TiO₂-based scales observed on the 10-3-1 and Ti-6242. The alumina scale formed on the 12.5-1.5 alloy because interstitials like O, N and C lower the thermodynamic activity of Ti to levels where Al₂O₃ formation is favored. In the absence of microstructural effects, the V in 10-3-1 prevented continuous external alumina from forming