Cloud Peak Energy Successful Bidder for West Antelope II South Coal Tract

Cloud Peak Energy Inc. (NYSE:CLD), one of the largest U.S. coal
producers and the only pure-play Powder River Basin (PRB) coal company,
today announced its successful bid for the West Antelope II South Coal
Tract, which was previously nominated by the company′s Antelope mine.
The Bureau of Land Management (BLM) estimates this tract contains
approximately 56 million tons of mineable coal. At year-end 2010, the
company′s Antelope mine had an estimated 252 million tons of coal
reserves, and Cloud Peak Energy had an estimated total reserve of 970
million tons of coal.

Cloud Peak Energy successfully won the lease sale with a bid of
approximately $49.3 million, or $0.875 per ton, based on the BLM′s
estimate of 56 million mineable tons. The company submitted a payment
for approximately $9.8 million, which is the first of five equal
payments for the federal coal lease. The BLM typically awards the lease
within several months after selecting a winning bidder. As previously
disclosed, the West Antelope II Lease by Application (LBA) is subject to
pending legal challenges filed by certain environmental organizations
against the BLM and the Secretary of the Interior.

On May 11, 2011, Cloud Peak Energy announced its successful bid for the
West Antelope II North Coal Tract, which the BLM estimates contains
approximately 350 million tons of mineable coal.

'We′re very pleased with our acquisition of the West Antelope II South
Coal Tract. Together with our recent successful bid for the West
Antelope II North Coal Tract, 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,? said Colin Marshall, President
and Chief Executive Officer.

About Cloud Peak Energy ^®

Cloud Peak Energy Inc. (NYSE:CLD) is headquartered in Wyoming and
is one of the largest U.S. coal producers and the only pure-play Powder
River Basin (PRB) coal company. As one of the safest coal producers in
the nation, Cloud Peak Energy specializes in the production of low
sulfur, subbituminous coal. The company owns and operates three surface
coal mines in the PRB, the lowest cost major coal producing region in
the nation. The Antelope and Cordero Rojo mines are located in Wyoming
and the Spring Creek mine is located near Decker, Montana. With
approximately 1,500 employees, the company is widely recognized for its
exemplary performance in its safety and environmental programs. Cloud
Peak Energy is a sustainable fuel supplier for approximately 4 percent
of the nation′s electricity.

Cautionary Note Regarding Forward-Looking Statements

This release contains 'forward-looking statements' within the meaning of
the safe harbor provisions of Section 27A of the Securities Act of 1933
and Section 21E of the Securities Exchange Act of 1934. Forward-looking
statements are not statements of historical facts and often contain
words such as 'may,' 'will,' 'expect,' 'believe,' 'anticipate,' 'plan,'
'estimate,' 'seek,' 'could,' 'should,' 'intend,' 'potential,' or words
of similar meaning. Forward-looking statements are based on management's
current expectations or beliefs, as well as assumptions and estimates
regarding our company, industry, economic conditions, government
regulations and energy policies and other factors. Forward-looking
statements may include, for example, (1) our estimates of proven and
probable coal reserves, future production and reserve life, (2) BLM′s
timing to award the coal lease for the West Antelope II LBA and the
timing of future LBAs, (3) our ability to obtain all required regulatory
permits and approvals to mine newly acquired coal tons in a timely and
cost-effective manner, (4) the impact of pending or future third party
litigation and regulatory challenges, (5) business development and
growth initiatives; and (6) other statements regarding our plans,
strategies, prospects and expectations concerning our business,
operating results, financial condition and other matters that do not
relate strictly to historical facts. These statements are subject to
significant risks, uncertainties, and assumptions that are difficult to
predict and could cause actual results to differ materially from those
expressed or implied in the forward-looking statements. For a discussion
of some of the factors that could adversely affect our future results,
refer to the risk factors described from time to time in the reports and
registration statements we file with the Securities and Exchange
Commission ('SEC'), including those in Item 1A - Risk Factors in our
most recent Form 10-K and any updates thereto in our Forms 10-Q and
current reports on Forms 8-K. There may be other risks and uncertainties
that are not currently known to us or that we currently believe are not
material. We make forward-looking statements based on currently
available information, and we assume no obligation to, and expressly
disclaim any obligation to, update or revise publicly any
forward-looking statements made in this release, whether as a result of
new information, future events or otherwise, except as required by law.

Cloud Peak Energy Inc.

Karla Kimrey, 720-566-2900

Vice
President, Investor Relations