The oxidation behavior of zirconium alloys used as materials for nuclear fuel rod claddings is investigated in the temperature range between 973 and 1673 K in steam and air atmosphere. Parabolic kinetics was found for all materials, atmospheres and temperatures, at least at beginning of the reactions. The temperature dependence of the reaction rate is of Arrhenius type. The parameters of the Arrhenius functions are determined and given for steam oxidation. Due to the formation of a large amount of cracks an acceleration of the reactions can occur. Reasons of the crack formations are phase transformations in the oxide layer known as the breakaway effect and, in case of air atmosphere, local oxygen starvation conditions resulting in reactions with nitrogen. The paper gives a short overview of the relevant mechanisms and processes.