Significant recent development in subsea design includes subsea processing, particularly removal of produced water from oil closer to the reservoir, with subsequent reinjection of this water. Significant effort is being put into separation and reinjection systems that are downhole or at the seabed. Subsea processing has been available for at least the last decade; however, major challenges exist related to process/flow assurance and other operability issues. Process-design efforts with the Troll pilot have minimized uncertainties and risks.