Time-lapse (4D) seismic data from Ringhorne Field in the North Sea are used to monitor water movement in both Paleocene- and Jurassic-age reservoir sands, improve existing geologic and simulation models, and enable more cost-effective field operations. The structural complexity of the reservoirs, their proximity to the high-impedance Cretaceous chalk, and a relatively small 4D response has required a significant effort in seismic acquisition and processing which resulted in highly repeatable surveys (Johnston et al., 2010). In addition to the 4D interpretation, VP/VS derived from simultaneous elastic inversion is diagnostic of sand and provides additional constraints on Ringhorne subsurface models. Connected volumes based on VP/VS correlate to areas of water sweep seen in the 4D data and reduce uncertainty in 4D interpretation. Relative P-wave impedance changes calculated from inversion are consistent with presurvey 4D predictions. The 4D seismic data and inversion help explain water breakthrough timing, improve our understanding of field production history, and have resulted in the identification of additional infill well opportunities.