The oxygen tracer diffusivity of CaZr0.9In0.1O2.95, SrCe0.95Yb0.05O2.975, and BaCe0.9La0.1O2.95 at a nominal oxygen partial pressure of 1 atm (P(H2O)similar to 10(-6) atm) has been measured in the temperature range 500-1000 degrees C by means of O-18/O-16 Isotope Exchange Depth Profiling (IEDP) with SIMS. The results are interpreted in terms of the ordering of oxygen vacancies in the orthorhombic structured perovskites. Negative secondary ion mass spectra (m/z=16 to 19) obtained from SrCe0.95Yb0.05O2.975 samples are also discussed, with particular reference to the presence of fluorine. Confirmation of fluorine contamination was provided by F-19 Proton Induced Gamma-ray Emission (PIGE) analysis.