Mr Don Argus chairman of BHP Billiton recently insisted that it is only his company's hostile bid for Rio Tinto that was propping up Rio's share price.

In a letter to Rio shareholders, Mr Argus said that the offer of 3.4 BHP shares for every Rio share was a 45% premium to Rio's share price.
He added that "This is a substantial premium by any measure, and one that is reflected in the large increase in the market for Rio Tinto shares, relative to BHP Billiton shares, since our proposal became public last November 2008. Without the benefit of our offer, Rio Tinto shares would be trading very differently."

Mr Argus said that he expected the process to be completed by the end of the year and urged Rio shareholders to accept the deal, which is aimed at capitalizing on a China driven resources boom.

He added that "Both BHP Billiton and Rio Tinto have world leading portfolios of large scale, low cost, long life assets that are highly complementary. In many cases, assets are jointly owned, neighboring or close by. This unique overlap offers substantial opportunities to save money and add value through managing the assets as one collective group under single ownership."

BHP's current 3.4 for one share offer was originally valued at USD 147 billion, but changes in share prices mean that it is now worth GBP 170 billion. Rio shares are currently trading above the effective offer price.