Instability of the catalysts during oxygen evolution reaction (OER) has been a major concern in technologies like electrocatalytic water splitting, rechargeable metal air batteries, and regenerative fuel cells. For many catalytic materials, a trade-off has been observed between activity and stability. In search of the fundamental understanding of this phenomenon, we investigated RuO_x as a model electrocatalyst using in-situ XAS in soft and tender x-ray regime, XPS, and ESEM using a graphene based confined electrolyte approach. The O K-edge absorption spectra probed the surface and the sub-surface oxygen species while the Ru L_3,2-edge absorption spectra mapped the average oxidation state of ruthenium sites at OER relevant potentials. The combined analysis hints towards the idea that OER is not only centered at the undercoordinated ruthenium (Ru_cus) sites but is a shared event which proceeds via the redox of both Ru_cus sites and surface oxygen atoms. The oxidation of the lattice O atoms during the water splitting process “activates” the whole lattice. We propose that this O-centered oxidation is the reason for the instability of the material during OER.