ABSTRACT In recent years, major advances have been made in understanding injection well performance. In particular, the impact of fracturing, thermal stress effects and water quality are far better understood, as a result of both improved theoretical understanding and from detailed analyses of field data. This paper reviews our current understanding of the processes which control the performance of injection wells, including the effects of produced water quality, taking examples mainly from the Prudhoe Bay and Forties oil fields. Techniques for predicting and optimising injector performance under a variety of circumstances are discussed, together with the implications for waterflood management.