The papers in this book represent the proceedings for the International Conference on Oxygen Disorder Effects in High Tc Superconductors, held April 18-21, 1989 at the International Centre for Theoretical Physics, Trieste, Italy. It was recognized very early in the field of ceramic superconductors that oxygen plays a crucial role as far as the physical properties of these ma terials are concerned. The preparation requires special heating and cooling cycles which allow proper uptake of oxygen, relationships were found between the oxygen concentration and the superconducting transition...