The use of time-lapse (4D) seismic at BP now has a track record stretching back more than 20 years. In the North Sea, reservoir types such as Tertiary turbidites and Cretaceous chalks produced clear 4D signals, and uptake increased rapidly in the late 1990s. In the Gulf of Mexico, 4D was generally more challenging due to greater subsurface complexity, but the industry made breakthroughs with modern acquisition systems such as ocean-bottom nodes (OBN). The challenge now is to maximize the value of existing and new surveys by better integration of 4D into reservoir management. As part of this effort, the authors implemented fit-for-purpose workflows for 4D-assisted history matching (4DAHM) and 4D geomechanical modeling. In an example from west of the Shetland Isles, UK, running the 4DAHM match-quality tool on multiple monitors from the Clair Field allows the field team to quickly see how changes in the reservoir simulation model affect the match to the 4D and identify areas of concern. The 4D geomechanics workflow utilizes the Geertsma equation to speed up modeling of effective stress changes due to compaction. It is demonstrated on the Gulf of Mexico Atlantis Field, where the authors were able to resolve a significant mismatch between the reservoir simulation model and observed seismic amplitude responses by modeling a strong stress-arching effect due to reservoir depletion.