It is believed better mapping of the Cook Islands' territories and borders could be worth trillions to the country's economy.
The Territorial Sea and Exclusive Economic Zone Amendment Bill, enabling more accurate mapping of the country's slice of ocean, has been unanimously adopted.
The Cook Islands' exclusive economic zone, which spans about two million square kilometres of ocean, could receive an additional 400,000 square kilometres as a result of the bill.
The deputy opposition leader Wilkie Rasmussen says it could also give back some of the territory the country used to claim, including Christmas Island.
Marine resources minister, Teina Bishop, says from a fisheries point of view the legislation change could be worth millions, while from a seabed minerals point of view could be in the trillions.
The re-defined borders may soon be put before the United Nations for formal recognition.