Toyota Tsusho said in a statement on Thursday that its subsidiary would take a 7.5% stake in the WA-294-P block, covering 4200 square kilometres, for an undisclosed sum.
Meanwhile, state-run Japan Oil, Gas and Metals National Corp (JOGMEC) said in a separate statement it would provide 75% of Toyota Tsusho's expected costs, or 864 million yen ($8.32 million), by 2010.
The permit is operated by Woodside Energy with a 42.7% stake, while Japan Australia LNG (MIMI) Pty Ltd has 32.4% and BHP Billiton 17.4%
The joint venture is reportedly planning to begin developing the permit in 2015.
Toyota Tsusho said any gas produced in the permit would be processed into LNG and exported to such countries as Japan and the US.
