On Wednesday, BG made an $A12.9 billion ($15.7 billion) takeover offer for Origin Energy which owns 51% of Contact.
Mr Timms said the offer represented a 40% premium on yesterday's opening price for Origin, and it was difficult to see the board knocking back a bid of 30 times 2008 full-year earnings.
"It's difficult to see who would be willing or even able to stump up more at this stage, '' he said.
"We believe some local Australian companies would love to have a crack at Origin but would be unlikely to raise the funding, especially post the credit crunch.''
Under the New Zealand takeovers law, a follow-on New Zealand code offer would need to be made to Contact shareholders unless there was an exemption given under the code, which was unlikely because Contact made up 36.5% of Origin's operating earnings.
BG might also structure its bid in a way which did not require a New Zealand follow-on offer, but that would require a Contact shareholder vote.
Another scenario could see a low offer designed to have BG group stay at 51.4% ownership of Origin, Mr Timms said.
"All of these scenarios are messy and very uncertain for BG.''
Additionally, an Overseas Investment Office application would be required, and ministerial approval under the sensitive land test would be needed.
However, when any deal was structured, ABN expected a premium to apply to Contact to ensure success of the BG proposal.
"We believe that BG will have a focus on Origin's upstream gas, liquefied natural gas and reserve assets, but we would expect some premium to market price to apply to Origin's Contact investment.''
Regarding the bid for Origin, Mr Timms said the best case for shareholders would be to see a rival bid emerging or the Origin board managing to squeeze more out of BG.
"Would BG go hostile if the Origin board played hardball, or would it just roll over and dole out another billion? We think the most likely outcome is that the current bid eventually gets up, but the process could easily drag out for six months,'' he said.
