While exploration geophysics remains important for locating resources, monitoring changes that result from production is becoming increasingly important for managing reservoirs. 4-D seismics is being developed to track where changes occur, geodetic observations of changes in surface deformation with time place constraints on subsurface and volume changes, while monitoring fluxes and pressures in wells provide strong constraints on the spatial distribution of flow properties. Each of these techniques is commonly used alone. What distinguishes research done at ERL is the way we combine multiple types of observations using quantitative models to provide better understanding of coupled processes in the subsurface.