Due to the multiplicity of problems recently evidenced by the widely used N2O decomposition technique, the oxygen chemisorption technique for the measurement of Cu surface area was updated and optimized. A standard procedure was defined, which allows to obtain reliable and reproducible data. In particular, no arbitrary assumption was made for the Cu/O chemisorption stoichiometry and for the degree of surface coverage. Conversely an experimental value of the average Cu/O surface ratio, including the degree of coverage, was determined by XRD-WAXS data. The value obtained (2.35) corresponds to a chemisorption stoichiometry Cu/O = 2 and to about 15% unoccupied surface Cu atoms. The proposed technique has been successfully used for the characterization of several commercial low-temperature water gas shift catalysts (Cu-ZnO-Al2O3).