My assets are better than your assets! That is the game miners Rio Tinto and BHP Billiton have been playing since the latter proposed a merger in November. In an all-share deal, expectations for relative earnings should influence the merger ratio. About 15 per cent of BHP’s 2009 earnings will be from coal, twice that of Rio. Therefore, this week’s news that the steelmakers Posco and ArcelorMittal have reportedly agreed to a tripling of coal contract prices helps BHP. Conversely, eye-popping iron ore prices move the terms in Rio’s favour.