A process for the production of diesters of oxalic acid by oxidative carbonylation of alcohols with carbon monoxide and oxygen as oxidizer at pressures of 1 to 700 atmospheres and in a temperature range between 20.degree. and 250.degree. C. in a reaction phase containing the alcohol and, as catalyst, palladium and at least one metal halide in catalytically effective amounts, whereby a catalyst system is used which consists of palladium, at least one metal halide, and an activated carbon which has been pretreated before use by heating to 200.degree.-1,500.degree. C. in a gas atmosphere G, differing from air.The gas atmosphere G, differing from air, consists, preferably, of at least one of the gases (a) nitrogen; (b) nitrogen compounds, except those with nitrogen-oxygen bonds; or (c) carbon monoxide; and may optionally contain an accompanying gas.