Time-lapse (4D) seismic can be effectively integrated into the reservoir-management process by embedding the calculation of seismic attributes in a flow simulator. This paper describes a petroelastic model (PEM) embedded in a multipurpose flow simulator. The flow simulator may be used to model gas, black-oil, compositional, and thermal systems. The PEM can calculate reservoir geophysical attributes such as compressional-wave (P-wave) and shear-wave (S-wave) velocities and impedances, dynamic and static Young's moduli, and dynamic and static Poisson's ratios. Examples illustrate how to use the PEM to facilitate the integration of 4D seismic and reservoir flow modeling. John R. Fanchi, SPE, is professor of petroleum engineering in the Department of Engineering and Energy Institute at Texas Christian U., Fort Worth, Texas, USA. He teaches courses in energy and engineering. Previously, Fanchi taught petroleum and energy engineering courses at the Colorado School of Mines, and worked in the technology centers of four energy companies, most recently at Chevron. He co-edited the General Engineering volume of the SPE Petroleum Engineering Handbook, and is the author of several books, including Energy in the 21st Century (World Scientific; 2005), Energy: Technology and Directions for the Future (Elsevier-