CANBERRA, Australia — Investors seem sure that mining giant BHP Billiton will continue its $149 billion pursuit of Rio Tinto, a combination that would control more than one-third of the world's iron ore sales.

Rio Tinto, which owns Kennecott Utah Copper, rejected BHP Billiton's 3-for-1 share offer Thursday, but share price movements in London and Australia indicate investors expect BHP Billiton to increase its offer, the bid to turn hostile or another bidder to emerge.

BHP said in an overnight statement confirming its approach to its mining rival that it "intends to continue to seek an opportunity to meet and discuss its proposal with Rio Tinto."

A combination would create synergies throughout both Anglo-Australian mining companies and increase the range of products they can market while eliminating duplication and competition, said Prof. Tony Naughton, a stock market and economics expert at Australia's RMIT University.

Dealogic PLC calculated BHP's offer to be worth $149 billion, which would make it the world's largest since Vodafone AirTouch's $172.2 billion takeover of German telecommunications company Mannesmann in a deal completed in 2000.

It would also eclipse Rio Tinto's $43 billion offer in May for Canada's Alcan Inc., the biggest deal involving a mining company to date.

Analysts say BHP may have to increase its 3-for-1 share offer to at least a 3.5-for-1 offer to encourage Rio to enter discussions.

"Will it go hostile? I don't know. I guess it depends on what other proposals BHP comes up with," said Warren Edney, an analyst with financier ABN AMRO.

A BHP Billiton spokeswoman said Friday there was nothing to add to Thursday's statement.

"We've rejected the proposal, and we've got nothing further to report," said Rio Tinto spokesman Ian Head.

Rio Tinto's objection to the deal is that it "significantly undervalues" the company, it had said in an earlier statement.

BHP Billiton, Rio Tinto and Brazil's Companhia Vale do Rio Doce, or CVRD, account for 70 percent of all global iron ore sales. BHP Billiton accounts for around 15 percent, with Rio Tinto responsible for 24 percent, which would give a combined company a 39-percent share of the world iron ore market.

Australia's competition regulator, Australian Competition and Consumer Commission, said Friday that concerns about dominance of Australia's iron ore market would be central to any investigation into a merger. The deal would need the approval of Australian regulators.