AbstractWet oxidation with molecular oxygen at mild conditions (temperature<200°C, pressure ⩽ 2 MPa) is an economically attractive pretreatment step for non‐biodegradable aqueous waste streams. In order to overcome the low reactivity of molecular oxygen towards organic molecules at these mild process conditions, an initiator was used in combination with ferrous ions in the acidic range. The promoted oxidation of phenol in aqueous solution was investigated in a 4 liters stirred autoclave. It was possible to degrade the phenol at temperatures as low as 100°C without observing an induction time. The remaining solution contained mainly acetic and formic acid and was well biodegradable.The oxidative behavior of the oxygen/phenol system could be explained using the well‐known autoxidation mechanism for aliphatic molecules. 4‐hydroperoxy‐phenol is suggested as a key intermediate. Measured products are p‐benzoquinone, hydroquinone, catechol, maleic, oxalic, pyruvic, formic, and acetic acid. Dinners could also be identified in sample extracts. A global pathway including all identified products