The solar selective properties of the copper oxides Cu20 and CuO on stainless steel have been studied. Copper oxide/stainless steel tandems have been prepared by thermal oxidation of sputtered copper films on sputtered steel films. The reflectance spectra for this type of tandem absorber show excellent agreement with calculated spectra. The calculations were performed with conventional optical interference formalism using the optical constants for the free oxides and polished stainless steel as input. For comparison copper films were also deposited by electrolysis from a copper sulphate solution. This preparation technique supresses the reflectance in the visible, which increases the solar absorption. It is suggested that the CuO/SS-tandem suffers less from thermal degradation than the CuO/Cu-tandem.