The BLM uses the secret figure to decide whether to accept or reject a high bid.
"They are bidding against the house and the house has a secret bid. So it is up to the company to put in their very, very best effort not knowing what our number is," BLM spokeswoman Beverly Gorny said.
The Cloud Peak release didn't offer details of its financial assessment of the coal tract and a company spokeswoman didn't return a message.
Spot coal prices have recovered somewhat from recent lows, said Wyoming Mining Association Executive Director Marion Loomis, but companies need to make long-term plans based on long-term contracts.
They need to be able to recoup their investment in expanding mines.
"It just shows the softness of the market right now. They don't want to make investments until they make sure there is a market available for that coal," Loomis said.