The investigation of 1 monolayer of oxygen on the Ru(1 0 (1) over bar 0) surface by directional elastic peak electron spectroscopy (DEPES) reveals high sensitivity of this surface method to light gases. The presentation of the experimental data as the anisotropy DEPES pattern shows an angular orientation of the oxygen adsorbate with respect to the substrate atoms. The straightforward identification of the oxygen structure is supported by a quantitative analysis providing oxygen atom coordinates within the unit cell. (C) 2012 Elsevier B. V. All rights reserved.