Rio Tinto PLC (RTP) shares Friday afternoon outperformed peers on continuing speculation that rival BHP Billiton Ltd. (BHP) could reemerge as a suitor in an effort to merge the Anglo-Australian miners.

"We feel there have been big changes since BHP Billiton walked from Rio Tinto last year and that the stars are now aligning for it to be able reach an agreed bid," Liberum Capital analyst Michael Rawlinson said in a note.

At 1539 GMT, Rio shares were up 93 pence, or 3.9%, at 2,474 pence, making it the best performing FTSE100 miner in a broadly weaker sector. The FTSE350 mining index was down 0.9%.

Rio Tinto last year spurned a takeover proposal from BHP offering 3.4 BHP shares for each Rio share. BHP in November walked away from that hostile bid, citing its rival's heavy debt and a sharp downturn in commodity markets.

Rawlinson said a new all-share offer at a ratio of about 2.5-to-1 would make sense for shareholders at both miners.

Spokesmen for BHP and Rio Tinto declined to comment on speculation surrounding a merger between the companies.

Renewed market interest in a merger emerged this week after Rio Tinto softened its tone on a proposed $19.5 billion investment from Aluminum Corp. of China, or Chinalco. Chief Financial Officer Guy Elliott said Rio has a "plan B" in place if the Chinalco investment faltered. The company also has a new chairman-elect, Jan du Plessis, sparking hope that the board could revisit the BHP deal.

Meanwhile, BHP in recent days has raised almost $5 billion in bond markets, fueling speculation it is ready to make an acquisition or to revisit its Rio bid.

"Rio ... is still the best deal for BHP in our view but BHP is not without options," said a trader who asked not to be named. Speculation has focused on acquisitions of potash, petroleum and iron ore producers.

The trader said BHP also would be interested in scuttling the Rio-Chinalco deal because it could put BHP at a competitive disadvantage in the Chinese market.

Rio earlier this year turned to Chinalco to help pay down about $38.7 billion in debt. Chinalco is set to invest $12.3 billion in minority stakes in a suite of Rio's iron ore, copper and aluminum assets. And it would buy $7.2 billion in convertible bonds that could increase its stake to 18% from around 9%.

Rio Tinto's management maintains that the investment is the best option for company. But it has met with intense shareholder opposition and potential regulatory hurdles.

BHP would also face regulatory issues to a renewed bid. It is prohibited by U.K. takeover law from launching a new offer for Rio until November, though the two sides could reach an agreed deal. European competition concerns also could hinder a deal.

Canaccord Adams analyst Damien Hackett said both Rio and BHP now know the terms of the objections raised by the European Commission and could structure a deal accordingly.

"It is worth remembering that the first all-share offer by BHP Billiton of 3 for 1 would translate today to GBP42/share for Rio Tinto. And, although we recognize the investment environment has changed a lot since then, we note it has changed for both. And the businesses are very similar," Hackett said in a note.

Company Web site: www.riotinto.com

-By Jeffrey Sparshott, Dow Jones Newswires; +44 (0)207 842 9347; jeffrey.sparshott@dowjones.com

(Kimberly Vlach contributed to this article.)