The aqueous-phase oxidation of formic acid and formate has been studied in a batch autoclave reactor at 260-degrees-C and 2 MPa of O2. The formate is converted to bicarbonate whereas formic acid, besides oxidation, decomposes by at least two different routes, namely a dehydration or a decarboxylation. In particular the second one is dependent on the reactor vessel used. It is shown to be catalyzed by a mixture of oxides of stainless steel components. The presence of CH3COOH or CH3CHO promotes the decomposition of HCOOH by way of both decarboxylation and oxidation. In any case formic acid is a relatively short-lived intermediate in the wet-oxidation process.