Thai Shell operates three onshore oil fields producing from the Yom/Pradu Tao Formations in the Phitsanulok Basin in Thailand: Sirikit D block, Thap Raet and Sirikit West. The Yom/Pradu Tao Formations originate from a low energy fluvial depositional environment with a low net-to-gross ratio of 20–40%. After a comprehensive evaluation of EOR methods, waterflooding was found to be the most attractive development concept to achieve a significant increase in recovery factor in the Yom/Pradu Tao reservoirs. However, waterflooding in a complex low net-to-gross fluvial environment is not straightforward. Thai Shell has followed a step-by-step approach in the implementation of waterflood starting with the Sirikit-D block in 2000, which is geologically least complex, followed by Thap Raet in 2001. Sirikit D block and Thap Raet are both showing a positive response to waterflooding, substantially increasing production and reserves. Sirikit West, the largest and geologically most complex of the three fields, has started water injection in May 2003. Prior to the implementation of waterflood in Sirikit West, the field had been subjected to extensive studies using multiple static and dynamic model realizations. This paper will provide an overview of the experiences and performance of waterflooding to date in the Sirikit-D and Thap Raet fields. In addition, it will explain the modeling approach and waterflooding plans in the Sirikit West field.