Plans to start production in the first quarter of this year were scuttled after BHP said in March that it had found an unspecified "anomaly" on the hull of the platform.

"The start-up of the Neptune project after several years of drilling, construction, and with the recent remediation work, is a significant accomplishment for BHP Billiton," BHP Billiton Petroleum chief executive Michael Yeager said.

Production is currently coming from one well and will increase as other producers are brought on line.

The Neptune tension leg platform is capable of producing up to 50,000 barrels of oil and 50 million cubic feet of gas per day.

The initial development consists of six subsea wells tied back to the platform.

More development wells are expected to be drilled after the acquisition and interpretation of new seismic data, which will be shot later this year.

The Neptune field consists of five blocks - Atwater Valley 573, 574, 575, 617 and 618 -located in water depths ranging from 1275-2000m.

Crude oil from Neptune is transported to markets via the Caesar pipeline (BHP 25% equity share) while gas is exported via the Cleopatra pipeline (BHP 22%).

BHP has a 35% operating interest in Neptune while Woodside holds 20%. Other partners are Marathon Oil (20%) and Maxus Exploration (15%).