Allen & Overy, Australia's Mallesons Stephen Jaques and New Zealand's Simpson Grierson are advising UK energy giant BG Group on its $13bn (£6.6bn) hostile takeover bid for Origin Energy, Australia's second-largest energy company, the American Lawyer has reported.

Clayton Utz is representing Origin, which has advised its shareholders to take no action on the bid.

The $13bn offer is BG's third bid for Origin and comes after Origin rejected an identical offer at the last minute in May. Origin said in May they believed the company was worth more than $13bn, especially in light of the $2.6bn (£1.3bn) merger between Malaysia's state oil company, Petronas, and Australian gas company Santos.

BG's chief executive Frank Chapman (pictured right) said that the Petronas transaction is "not relevant" to his company's offer for Origin, and that $13bn is likely to be as high as BG will go.

The offer amounts to $15.50 (£7.90) for each share of Origin stock. BG's initial offer, placed in April, valued Origin at about $14.70 (£7.50) per share. At that time, Origin's stock was trading at just over $10 (£5.10) per share, but the price has jumped to more than $16.40 (£8.30) as investors predict that Origin will receive a better takeover offer.