Abstract: A retrievable tree cap for use on a subsea tree having a concentric bore. The tree cap may be installed and retrieved using a remotely operated vehicle. Hydraulic pressure may be used to lock the tree cap onto the subsea tree and to set the tree cap seals. The tree cap is locked onto the subsea tree before setting the seals within the concentric bore. The tree cap includes a locking means that may engage a profile within the subsea tree regardless of the radial orientation of the tree cap. The tree cap may be used to hydraulically isolate an annulus bore from the production bore of the subsea tree. The tree cap may provide for the injection of a corrosion inhibitor within a cavity of the tree cap and may also provide for the removal of water trapped between the tree cap and the subsea tree.