The elevation of the oil/water contact within the massive Sarir field, located in the Sirte basin of Libya, is relatively uniform, suggesting continuous communication of the reservoir over the entire field. Yet, preliminary injectivity tests and drilling of peripheral injectors suggested otherwise. In some cases injection of water was found to he poor and distribution of fluid did not appear uniform. Also, the location of some peripheral injectors was well within the productive limit because the water/oil contact was poorly defined.