SummaryIn valley and blanket‐bog peat, oxygen‐diffusion rates and corresponding oxidation‐reduction potentials have been measured, and the relationship between them expressed graphically.Oxygen‐diffusion rates were obtained ‘polarographically’, and the Pt cathode also served as the redox indicator‐electrode.Plateau‐shifts towards more positive potentials made it necessary to use the reduced voltage setting of −0.48 v for oxygen determinations. These plateaushifts correlate with a lowering of the oxygen content, and an increase in acidity, or, perhaps, with the type of buffer systems found in peat.The ratio redox potential/oxygen diffusion is not constant. At very low oxygen values there is a relatively large increase in redox potential per unit of oxygen, but, as oxygen approaches 2 × 10−8g O2cm−2min−1, the ratio becomes much lower, while variations become more obvious.rH values calculated according to Jeffery (1961), show that, in peat of high iron content at pH 6, the first traces of oxygen correspond to an rH 1.10–1.20 (E6, 50–120; reduced and oxidized iron probably present), while above 2 × 10−8g O2cm−2min−1the rH is greater than 1.20 and oxidized iron probably predominates. Thus oxidized soil, as defined by Jeffery, may be maintained at very low oxygen levels.It is suggested that oxygen diffusing from plant roots into these peats will oxidize reduced soil prod