The company said the tract, nominated by its Antelope mine, contained an estimated 56 million tons of mineable coal.
It won the lease sale with a bid of about $US49.3 million, or $0.875 per ton based on the BLM reserve estimate.
Cloud Peak has already submitted a payment of about $9.8 million, the first of five equal payments for the federal lease. The BLM usually awards leases within several months following bidder selection.
The West Antelope II Lease by Application is subject to pending legal challenges filed by environmental organizations; these actions are against the state agency and the US Secretary of the Interior.
As of the end of 2010, the company's Antelope mine had an estimated 252Mt of coal reserves. Cloud Peak had an estimated total coal reserve of 970Mt at that time.
Last month, Cloud Peak successfully bid on the West Antelope North tract, which contains about 350Mt of mineable coal. The BLM will continue to hold federal lease auctions through the remainder of the US summer.
"Together with our recent successful bid for West Antelope II North, these tracts are expected to more than double the reserves at the Antelope mine and, along with the additional coal within an existing state of Wyoming lease near our Antelope mine, add more than 12 years of production," Cloud Peak president and chief executive officer Colin Marshall said.
Cloud Peak Energy is one of the top US coal producers and is the only pure-play Powder River Basin coal company. It owns and operates three surface coal mines, the Antelope and Cordero Rojo mines in Wyoming and the Spring Creek mine near Decker, Montana.