A prized $120 million CSIRO ship built to study marine science has been hired out to international energy giants Chevron and BP to help them search for oil and gas in the Great Australian Bight.

Under the deal the ship Investigator is to spend two months working for the multinational corporations in the Southern Ocean, filling a period where it would have otherwise sat idle because of a lack of government funding.

All at sea?: Australia's marine science flagship, RV Investigator. Credit:CSIRO

The arrangement drew opposition from critics worried that the ship meant to vault Australia into the global marine science big league was being used for commercial, rather than institutional, research.

It also lands Investigator amid a controversy over the exploitation of the Bight's waters, where a marine reserve straddles the leases.