Interpretation of the energetic neutral atom data from the ASPERA-3 instrument aboard the ESA Mars Express spacecraft requires knowledge of the relevant charge-changing atomic collision cross sections. Important among these are collisions involving energetic O atoms, and absolute cross sections are reported here for electron capture and loss by 1--5 keV oxygen atoms incident on CO and CO2 for scattering angles between 0.02¿ and 1.73¿ in the laboratory frame. All of the differential cross sections are forward peaked, but those for electron loss decrease particularly slowly with scattering angle at low energies indicating that many of the colliding particles suffer significant deviation.