The galvanostatic oxidation of methanol-containing formaldehyde solutions, under conditions of simultaneous oxygen evolution, in 0.5 M H2SO4 acid was studied using a Ti/Ru0.3Ti0.7O2 dimensionally stable anode (DSA(R)), in a filter-press cell. The reaction products detected were HCOOH, CO2 and CO32-. The CO32- species is formed from the oxidation of HCOOH and subsequently decomposes in solution to CO2. Conversely CO2 is also formed electrochemically from the electrooxidation of formaldehyde and methanol. A mechanism, which considers the 'active' and 'non-active' nature of the electrode, is suggested. First-order kinetics, with respect to the variation of formaldehyde and methanol, are displayed and two linear regions observed. This is interpreted as being due to the presence of the reaction products of oxidation inhibiting the oxidation of formaldehyde at the electrode surface. Further, a mechanism is proposed considering the species present in solution.