Japan's second-biggest trading house said the deal would raise its stake to 35 per cent and that its total investment in the oil fields would be about $US140 million, including the cost of raising its stake. The Tui fields are estimated to hold about 27 million barrels of recoverable oil and production is expected to start by mid-2007. Other partners are Australia Worldwide Exploration Ltd, currently with 20 per cent, New Zealand Oil & Gas Ltd, with a 12.5 per cent stake, and Australian-based Pan Pacific Petroleum, with 10 per cent. After Mitsui raises its stake, a move subject to New Zealand government approval, Australia Worldwide Exploration will acquire NZOP, increasing its stake to 42.5 per cent, Mitsui said. Ahead of the announcement, shares in Mitsui closed up 0.51 per cent at 1,568 yen. The Nikkei share average gained 1.93 per cent. PIN/STUFF.CO