It told the Oslo Stock Exchange it had exercised a purchase option for the 78,489-cbm Berge Summit (built 1990).
It will use cash to pay the $8m bill for the veteran ship.
The book value, however, is expected to be $23m on delivery in May, including unamortised lease rentals and dry-docking expenses.
BW said: "The vessel will continue to be available for employment within our contract portfolio."
