Abstract: An oil recovery and storage ship having a general tank configuration of a conventional crude oil carrier is modified by providing inlet doors along opposite sides of the ship and a deployable floating boom arrangement for maximizing the floating oil gathering swath. The side inlet doors open into sluice or sea-calming compartments which have adjustable weir doors opening into primary separation tanks on port and starboard sides. Adjustable weir doors open from the primary separation tanks into a secondary separation tank. A selected number of cargo tanks are interconnected by conduits which permit the flow of liquid from one tank to the next in a series or cascade manner to decant oil from oily water and to discharge substantially oil-free water overboard from the last tank in the cascade. The ship may be used as a conventional liquids carrier when not required for oil spill recovery operations.