Zirconium oxidation was investigaied in the temperature range 400 io 900 deg C at oxygen pressures of 50, 200, and 800 mm. The reaction rate of massive (parallelepiped) samples was best expressed by the cubic rate law. At an oxygen pressure of 200 mm the activation energy was calculated to be 42.7 kcal per mole, and the cubic rate constant in ( mu g per sq cm) per minute can be expressed as k = (5.94 x 10/sup 16/)e/sup -42//sup ,70//sup 0//s/sup T/. The oxidaiion rate was found to be relatively insensitive to various types of surface preparations in ihe temperature range 400 to 700 deg C. No dependence of reaction rate on oxygen pressure was observed. The cubic rate law also was obeyed by foil specimens at 700 deg C; however, the rate constants were slightly larger than values obtained from parallelepiped samples. The oxidations of zirconium binary alloys containing nominally one, two, and four atom% additives of aluminum, beryllium, carbon, chromium, cobalt, copper, hafnium, iron, lead, molybdenum, nickel, niobium, platinum, silicon, tantalum, tin, titanium, tungsten, uranium, and vanadium were studied at 700 deg C and 200 mm oxygen. The alloys were grouped according to four types of oxidation behavior. Two groups consisted of alloys which oxidized according to the cubic rate law (Group I) or parabolic rate law (Group II) and did not exhibit breakaway phenomena. The other groups were alloys which initially oxidized according to the cubic rate law (Group III) or parabolic rate law (Group IV) but later exhibited breakaway oxidation phenomena. For alloys of those additives which are soluble in zirconium the initial oxidation rates are explained according to a valency effect in terms of the Wagner-Hauffe theory of alloy oxidation. For additives insoluble in zirconium, no single theory is felt to be adequate. The breakaway phenomena observed for many of the alloys is explained in terms of a 15% deviation of the additive ionic radius from the ionic radius of Zr/sup 4+/. Some x-ray and electron diffraction ...