Water vapor has significant effects on high temperature oxidation behaviors of high temperature alloys, especially on chromia-forming alloys due to oxidative evaporation of chromia scale. The objectives of this work are to study high temperature oxidation behaviors of commercial high temperature alloys, including seven chromia-formers, such as N06230, R30188, N08120, N06002, N06625, N06617, S34700, and three alumina-formers, such as N07214, NiCoCrMoAl, NiFeCrAl, at the temperatures from 760 to 1093°C (1400 to 2000°F) for up to one year exposure in the air atmospheres containing (5-30)% water vapor. The effects of water vapor content, temperature, heating/cooling condition, and alloy composition were analyzed from the results of metal loss and internal oxidation penetration, along with comparison with their oxidation behaviors tested in air without water vapor addition. The study shows, in general, water vapor could accelerate oxidation attack, and higher water vapor contents could cause more oxidation attack. However, high temperature oxidation behaviors of high temperature alloys will depend on multiple factors that need to be considered, especially when comparing oxidation results generated under different testing conditions.