The oxidation of Zr in air at elevated temperatures (T = 600 & 700 degrees C) was studied by in situ X-ray diffraction. The oxide scale consists of both tetragonal and monoclinic ZrO2 (tet- and mon-ZrO2 respectively). With increasing oxidation time, the layer gets thickened and tet-ZrO2 continuously transforms-to mon-ZrO2 due to the relaxation of the compressive stress in the oxide layer. The growth kinetics of the oxide scale and depth resolved texture of the oxide were determined. The kinetics of oxidation of zirconium can be described well by considering both the compressive strain energy gradient and the oxygen potential gradient as driving forces. (C) 2013 The Electrochemical Society. [DOI: 10.1149/2.006304jes] All rights reserved.