When is $39 billion is not enough?
BHP's close rival, Rio Tinto, is a possibility, but seen as an unlikely candidate. The $39 million offer is the world's highest bid across the board this year.
Both Rio and BHP are facing speculation their $116 billion iron ore joint venture won't get regulatory approval, which would lead to a $5 billion loss in cost savings for BHP, the world's largest mining company.
Potash is exploring potential alliances with global chemical and agricultural companies, and also Chinese sovereign banks, says the Wall Street Journal.