Yttrium-barium-cobalt-oxide (YBC), especially with low Y content, has been prepared. Oxygen permeation in these materials is very high at moderate temperature. The materials Y0.05BaCo0.95O3-delta and Y0.10Ba0.90CoO3-delta consisted of a BaCoO3-delta like main phase and some minor phases. For the Y0.05BaCo0.95O3-delta material these minor phases were not exceeding 10 vol%. Y0.05BaCo0.95O3-delta had the highest oxygen permeation value of 3.9 x 10(-7) mol/cm2 s at 900-degrees-C; the surface exchange reaction may be the rate limiting step here. The material Y0.33Ba0.67CoO3-delta consisted mainly of two unknown cubic phases.