Total photon mass attenuation of six multielement shielding materials (concrete, plaster of paris, quick lime, black cement, white cement, and silica) is measured in the 123- to 1250-keV energy range. The experimental results are analyzed in terms of cross sections, effective atomic numbers, and electron densities. Considerable sensitivity of the total mass attenuation coefficients and effective atomic numbers to variations in oxygen content are found in these multielement materials.