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The stopping of 1-2-MeV α particles in five solid oxides, MgO, Al2O3, SiO2, α-Fe2O3, and Fe3O4, has been investigated by measuring the ratios of the elastically-back-scattered-particle yields from two-layered metal-oxide and metal-metal targets. By applying a self-consistent analytical procedure, it is demonstrated that within the 2% sensitivity of the experiment, there is a unique set of five elemental stopping cross sections that is applicable to the pure metals and their oxides. When the effective stopping cross section of oxygen in these solid oxides is calculated using the reported Mg, Al, Si, and Fe stopping cross sections, the resulting values are systematically (6-22)% lower than the value reported for gaseous O2.