A subsidiary of ExxonMobil Corp. and BHP Billiton Ltd on Friday announced a $1.25 billion project to tap oil and gas reserves in Bass Strait off southern Australia.

The joint venture will build an offshore platform off Victoria state at a site called the Turrum field, and aims to extract about one trillion cubic feet of natural gas and 110 million barrels of oil and gas liquids, the companies said.

The Turrum project is expected to start producing from 2011, with gas sales from 2015.

ExxonMobil Australia chairman Mark Nolan said the Turrum project had enough resources to supply a city of one million people for longer than 20 years.

The announcement comes seven months after ExxonMobil and BHP Billiton approved the $1.1 billion development of another gas project nearby, called Kipper.