We studied the HOR/HER on polycrystalline Pt in alkaline electrolyte (0.1 M NaOH + 0.4 M NaClO 4 ) using the RDE technique under various hydrogen partial pressures. The results demonstrate that RDE analysis at different hydrogen pressures should be performed on a fixed potential scale, while the commonly employed overpotential scale can be misleading in terms of the apparent reaction orders, the assessment of the applicability, or non-applicability, of Koutecky-Levich mass-transport corrections, and the assignment of a certain reaction mechanism.