Many DFT studies of O2 dissociation on Pt(111) give conflicting information on preferred paths and final states. Here we report large p(4 × 4) unit cell minimum energy pathway evaluations and compare O2 adsorption and dissociated states on Pt(111). Calculations reveal how the pathways for O2 dissociation starting from top-fcc-bridge, top-hcp-bridge, and top-bridge-top sites are interconnected. They also provide a direct reaction pathway for the dissociation of an O2 molecule from a top-fcc-bridge into an hcp and an fcc site, which is consistent with low temperature scanning tunneling microscope experiments. Such a pathway is shown to be considerably perturbed by the presence of co-adsorbed oxygen atoms. We quantify the coverage dependence through the construction of a Brønsted–Evans–Polanyi relationship relating the O2 dissociation activation energies to the binding energies of the dissociated O atoms. We also show that all pathways starting from a top-fcc-bridge site give the smallest barriers for O2 dissociation.