BHP Billiton Ltd. (BHP) Chief Executive Marius Kloppers Wednesday said only a few companies are capable of assembling the kind of financing needed to compete with the company's unsolicited all-cash $38.6 billion offer for Potash Corp. of Saskatchewan Inc. (POT).

Asked in an interview on CNBC about speculation that BHP might have to increase its offer should a competitor emerge, Kloppers said the size of the transaction means few companies would be able to mount a challenge.

"I've seen the same speculation," said Kloppers.

"This is a large transaction, though. We've fully financed it. There's not an infinite universe of potential bidders, and for now our bid is the only one of the table.

"We keep on watching closely, but I haven't seen anything else yet."

"Only a few players are capable" of making an offer in the neighborhood of $40 billion, he said.

As for regulatory concerns, Kloppers said the company "feels comfortable" that it has assessed regulatory risks, and "this is an imminently doable transaction."

BHP last week took its offer directly to Potash shareholders after the Potash board said the offer was "grossly inadequate."