We have studied the relative diffusion rates of oxygen through dielectric/buffer layers used in high critical temperature superconducting multilayer structures. Epitaxial bilayer films of dielectric (CeO2, LaGaO3, NdGaO3, LaAlO3, MgO, SrTiO3, LaLiTi2O6, or LaNaTi2O6) on YBa2Cu3O7−δ (YBCO) have been deposited onto (001) oriented single-crystal MgO substrates using pulsed laser deposition. These bilayers have been investigated for oxygen diffusion over the temperature range 350 to 650 °C by postdeposition annealing the films for 20 min in 0.5 atm of 18O enriched molecular oxygen gas. Secondary ion mass spectroscopy was used to depth profile the relative concentration of 18O to 16O in each bilayer. Compared to YBCO, the dielectrics MgO, SrTiO3, LaLiTi2O6, and LaNaTi2O6 are relatively slow diffusers, while CeO2, LaGaO3, NdGaO3, and LaAlO3 are relatively fast diffusers.