The electrochemical transfer of oxygen was investigated for electrode negative and electrode positive polarities in the submerged arc, shielded metal arc and gas tungsten arc welding processes. Analysis of the welds showed that electrochemical reactions as well as thermochemical reactions are significant in altering the oxygen content of the weld metal. The oxygen transfer in the submerged and shielded metal arc welding processes is strongly influenced by electrochemical reactions at the slag/metal interface, and oxygen transfer in gas tungsten arc welding is strongly influenced by electrochemical reactions at the plasma/metal interface. The electrochemical oxygen reactions at the slag/metal interface include oxygen pickup at the anode and oxygen refining at the cathode. Electrochemical oxygen reactions at the plasma/metal interface include the refining of oxygen at the anode and pickup at the cathode. Electrochemical reactions have the greatest influence on weld metal chemistry at high welding currents and at slow weld travel speeds.