Transition-metal perovskite oxides are being investigated as catalysts and electrocatalysts for reactions such as aqueous oxygen evolution and elevated-temperature oxygen incorporation. These oxides are characterized by their tendency to exhibit cationic, anionic and electronic disorder, such as Schottky defect pairs, oxygen vacancies, and small polarons, respectively. When present in significant concentrations, these defects alter the phase stability of the near-surface region, reactivity, and carrier transport. We have investigated a range of Ti, Co, and Fe-based materials using high-resolution transmission electron microscopy, in-situ X-ray photoemission spectroscopy and X-ray absorption spectroscopy. In this talk, I will discuss the role of these lattice disorder in catalysis and electrocatalysis involving oxygen molecules.