The influence of at% Mn on the polarization and spontaneous passivation of (CoCrFeNi)100-xMnx (at%) alloys in aerated 0.1 M H₂SO₄ was investigated using atomic emission spectroelectrochemistry. At 0 – 6.5 at% Mn, spontaneous passivation occurred but at ≥ 10 at% Mn, the beneficial effect of Cr was completely negated. Spontaneous passivation could be predicted from Evans diagrams in which total current was decoupled into anodic dissolution and the cathodic components. Passivation occurred in two stages: rapid reaction with significant Cr enrichment; slower reaction with less enrichments. Differences between spontaneous and potentiodynamic passivation are discussed and interpreted with rate vs. free potential curves.