Hyde is a small, low-permeability gas field in the U.K. southern North Sea, which has been developed using horizontal wells. Shortly after production startup in Sept. 1993, the field performance began to give cause for concern. Both wells were producing formation water, and the gas deliverabilities were lower than predicted. This paper described how field data were collected, analyzed, and used in a full-field simulation model to diagnose the cause of the poor performance and to plan the future development of the field.