Pt 3 Ni (1 1 1) is the most efficient catalyst for the oxygen reduction reaction. Herein, we investigated the oxidation process of Pt 3 Ni (1 1 1) by time‐resolved X‐ray photoemission spectroscopy experiments with synchrotron radiation. For O 2 exposure at room temperature, two well‐distinct O species are present with a sticking coefficient of 0.23–0.24 in the temperature range of interest for fuel‐cell technology. We show that the Pt skin of Pt 3 Ni (1 1 1) is selectively replaced by Ni 2 O 3 and NiO surface‐skin layers upon heating in an O 2 environment at 700 and 900 K, respectively. By dosing with O atoms, the formation of PtO is possible at 293 K, whereas Ni 2 O 3 is formed at 353 K.