TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractManagement of mature oil fields requires accurate formation evaluation information. The ability to acquire essential data through casing adds a new dimension to reservoir characterization and affects the reservoir development of a mature oilfield like the Bahrain field. New logging tools and technology fill the gap in evaluation, especially for monitoring water saturation changes over time and for detecting bypassed oil pockets across the zone.In this paper we present the results and validity of a logging through casing run in a depleted well completed in a sandstone reservoir in the Bahrain oilfield. The reservoir has a complex lithology of high-permeability sandstone with thin interbeds of siltstone and shale, erratically deposited but prolific in oil production. The objectives of the data acquisition were to monitor oil depletion through casing and to study the effect of lithology on the water encroachment pattern across the zone.In this paper we describe the interpretation procedures and data validation of the information obtained from an advanced suite of logs run through casing. The paper also focuses on how this new information has resulted in a review of potential further development of this pay in one part of the field.