Time-lapse 3D, also known as 4D, seismic data were incorporated into the modeling and management of the Andrew and Harding reservoirs. These fields pose similar challenges in that both use horizontal wells to produce from a 160- to 330-ft-thick oil column between a gas cap and an aquifer. Therefore, seismic data must be used to determine the vertical movement of fluid contacts in different areas. These fields also have important differences, notably in vertical communication and aquifer strength, and demonstrate a range of data applications and consequences.