PotashCorp's Board of Directors Rejects BHP Billiton's Unsolicited, Non-Binding Proposal as Grossly Inadequate

SASKATOON, Canada, August 17, 2010 - Potash Corporation of Saskatchewan Inc. ("PotashCorp") today
announced that its Board of Directors has received and unanimously rejected
an unsolicited proposal from BHP Billiton Limited
("BHP Billiton") to enter into a transaction under which BHP Billiton
would acquire PotashCorp for US$130 per share in cash. PotashCorp's Board of
Directors thoroughly reviewed BHP Billiton's unsolicited proposal with the
assistance of its independent financial and legal advisors and concluded that
the proposal is grossly inadequate and it is not in the best interests of its
shareholders for PotashCorp to enter into discussions with BHP Billiton.

"The PotashCorp Board of Directors unanimously believes that
the BHP Billiton proposal substantially undervalues PotashCorp and fails to
reflect both the value of our premier position in a strategically vital
industry and our unparalleled future growth prospects," said PotashCorp
Chairman Dallas J. Howe. "After careful consideration, and in the interest of
transparency, our Board determined to proactively disclose BHP Billiton's
unsolicited, non-binding proposal to our shareholders. We believe it is
critical for our shareholders to be aware of this aggressive attempt to
acquire their company for significantly less than its intrinsic value. The
fertilizer industry is emerging from the recent global economic downturn, and
we feel strongly that PotashCorp shareholders should benefit from the current
and potential value of the Company. We believe the BHP Billiton proposal is
an opportunistic effort to transfer that value to its own shareholders."

PotashCorp President and Chief Executive Officer Bill Doyle
commented, "Global demand for food is steadily increasing, creating an
attractive operating environment for the entire fertilizer industry and, with
our premier position, PotashCorp is uniquely poised to benefit. We believe
our Board and management team are successfully executing our business plan
and producing strong results. With our unmatched asset base and proven
strategies, we believe we are well positioned to exceed the expectations of
customers around the world and deliver compelling value to our shareholders."

In making its determination, the PotashCorp Board of Directors
considered a number of factors including:

The BHP Billiton Proposal Fails to Reflect PotashCorp's
Prospects for Continued Growth and Shareholder Value Creation: PotashCorp
is poised to deliver strong earnings growth as agricultural fundamentals
continue to strengthen, global demand for its products - especially
potash - increases, and its strategic investments in new potash capacity
uniquely position it to capture a disproportionate share of demand
growth. The Company firmly believes it is on the verge of an inflection
point, where potash demand will return to historical trend-line growth,
supply will tighten, and pricing will improve. The powerful long-term
drivers of the fertilizer business - population growth and improving
diets in developing nations - changed little as a result of the global
downturn, and the catalysts expected to fuel near- and medium-term demand
are accelerating. A rising demand for food - coupled with historically
low global grain inventories - support a powerful period of growth for
agriculture. The PotashCorp Board believes that no other company is
better positioned to capitalize on these growth opportunities. The Board
is confident that PotashCorp can deliver significantly greater value to
its shareholders than BHP Billiton's inadequate proposal.

PotashCorp is a Uniquely Valuable Asset: PotashCorp is
uniquely positioned as the premier global producer with unparalleled
potash assets in an industry characterized by substantial barriers to
entry, few producers and no known product substitutes. The BHP Billiton
proposal fails to adequately compensate PotashCorp shareholders for this
strategic position and scarcity value. In addition, the BHP Billiton
proposal does not reflect PotashCorp's substantial recent and ongoing
investments to increase capacity, the value of PotashCorp's strategic
equity investments in China, Chile, Jordan and Israel, and its unmatched
ability to meet the needs of North American customers and growing
offshore potash markets.

The BHP Billiton Proposal Represents a Wholly Inadequate
Premium For Control: At US$130 per share, BHP Billiton is proposing a
premium of only 16% over PotashCorp's August 16, 2010 closing stock
price. This low premium does not reflect the strategic importance,
scarcity value and quality of PotashCorp's assets, or the unique
opportunity PotashCorp affords to BHP Billiton or any other acquiror.
Furthermore, the premium offered is substantially inferior even to
average control premiums globally and in Canada.

The BHP Billiton Proposal is Timed to Deprive PotashCorp
Shareholders of Full Value: BHP Billiton is opportunistically attempting
to transfer the upside value in PotashCorp to its own shareholders at the
expense of PotashCorp shareholders. PotashCorp believes the timing of the
BHP Billiton proposal is highly opportunistic and an ill-disguised
attempt to exploit an anomaly in the equity market valuation of
PotashCorp. PotashCorp believes that BHP Billiton intentionally launched
its proposal just as the fertilizer industry emerges from an
unprecedented demand decline associated with the global downturn in order
to seize the value that PotashCorp is poised to create. The Company is
confident that, given the demand growth and margin potential anticipated
in the months and years ahead, the continued execution of PotashCorp's
strategic plan would deliver substantially more value to PotashCorp
shareholders than the BHP Billiton proposal.

The Board of Directors communicated its response to BHP
Billiton in a letter sent to its Chairman of the Board on August 17, 2010,
the full text of which follows:

    August 17, 2010

    Jacques A. Nasser
    Chairman of BHP Billiton Limited
    BHP Billiton Centre
    180 Lonsdale Street
    Melbourne, VIC 3000
    Australia

    Dear Mr. Nasser:

    The Board of Directors of Potash Corporation of Saskatchewan
    Inc. (PotashCorp) has reviewed your August 13, 2010 letter proposing that
    PotashCorp and BHP Billiton enter into discussions regarding a
    transaction in which BHP Billiton would acquire PotashCorp at US$130 per
    share in cash.

    After carefully and thoroughly reviewing the contents of your
    unsolicited proposal, with the benefit of advice from our financial and
    legal advisors, we have unanimously concluded that your proposed price
    grossly undervalues PotashCorp and its strong prospects for continued
    growth and shareholder value creation.

    In particular, we believe the timing of your proposal is
    highly opportunistic given that, among other things, the industry is
    still in the early stages of a recovery. In our view, PotashCorp is
    significantly and disproportionately undervalued as a result of our
    strategic decisions to match production with demand while continuing to
    invest in our infrastructure. The Board determined that your proposal
    fails to adequately recognize the value of PotashCorp's premier position
    in the industry, the value of our planned capacity expansions and the
    value of our equity investments.

    The PotashCorp Board strongly and unanimously believes that
    PotashCorp has a bright future as an independent company and nothing in
    your August 13, 2010 letter provides the basis for PotashCorp to alter
    its course. Accordingly, we do not believe the proposed transaction is in
    the best interests of our shareholders. As we are committed to open,
    transparent treatment of our shareholders and other stakeholders, we are
    making your proposal and our response publicly available.

    Sincerely,

    /s/ Dallas J. Howe

    Dallas J. Howe
    Board Chair

BofA Merrill Lynch, Goldman, Sachs & Co. and RBC Capital
Markets are acting as financial advisors to PotashCorp and Jones Day and
Stikeman Elliott are acting as its legal advisors.

About PotashCorp

Potash Corporation of Saskatchewan Inc. is the world's largest
fertilizer enterprise by capacity producing the three primary plant nutrients
and a leading supplier to three distinct market categories: agriculture, with
the largest capacity in the world in potash, third largest in each of
nitrogen and phosphate; animal nutrition, with the world's largest capacity
in phosphate feed ingredients; and industrial chemicals, as the largest
global producer of industrial nitrogen products and the world's largest
capacity for production of purified industrial phosphoric acid. PotashCorp's
common shares are listed on the Toronto Stock Exchange and the New York Stock
Exchange. As of June 30, 2010, 49.03% of the common shares were held in
Canada, 37.59% of the common shares were held in the United States and 13.38%
of the common shares were held outside of Canada and the United States.

This release contains forward-looking statements or
forward-looking information (forward-looking statements). These statements
are based on certain factors and assumptions including foreign exchange
rates, expected growth, results of operations, performance, business
prospects, evaluations and opportunities and effective income tax rates.
While the company considers these factors and assumptions to be reasonable
based on information currently available, they may prove to be incorrect.
Several factors could cause actual results to differ materially from those
expressed in the forward-looking statements, including, but not limited to:
future actions taken by BHP Billiton in connection with its unsolicited,
non-binding proposal; fluctuations in supply and demand in fertilizer,
sulfur, transportation and petrochemical markets; changes in competitive
pressures, including pricing pressures; the recent global financial crisis
and conditions and changes in credit markets; the results of sales contract
negotiations with China and India; timing and amount of capital expenditures;
risks associated with natural gas and other hedging activities; changes in
capital markets and corresponding effects on the company's investments;
changes in currency and exchange rates; unexpected geological or
environmental conditions, including water inflow; strikes and other forms of
work stoppage or slowdowns; changes in and the effects of, government policy
and regulations; and earnings, exchange rates and the decisions of taxing
authorities, all of which could affect our effective tax rates. Additional
risks and uncertainties can be found in our Form 10-K for the fiscal year
ended December 31, 2009 under captions "Forward-Looking Statements" and "Item
1A - Risk Factors" and in our other filings with the US Securities and
Exchange Commission and Canadian provincial securities commissions.
Forward-looking statements are given only as at the date of this release and
the company disclaims any obligation to update or revise the forward-looking
statements, whether as a result of new information, future events or
otherwise, except as required by law.

    ________________________________________________________________________

          PotashCorp will host a conference call on Tuesday, August 17,
                        2010 at 8:30 am Eastern Time.

           A slide presentation will accompany the conference call and
                   will be available on the Company's website.

          Please note the appropriate dial-in number for your location
                                    below
              and call at least 10 minutes prior to the start time.

                         No reservation ID is required.

                 **********************************************

                        From Canada dial: 1-877-354-7102
                          From USA dial: 1-877-902-6545
                      From elsewhere dial: +1-412-902-6510

                 **********************************************

       Alternatively, visit www.potashcorp.com for a live webcast of
                            the conference call.

          This news release is also available on the Company's website.

    For further information, please contact:

    Investors
    Denita Stann
    Senior Director, Investor Relations
    Phone: +1-847-849-4277
    Email: ir@potashcorp.com

    Media
    Bill Johnson
    Director, Public Affairs
    Phone: +1-306-933-8849
    Email: pr@potashcorp.com

    Eric Brielmann / Jamie Moser / Andrew Siegel
    Joele Frank, Wilkinson Brimmer Katcher
    Phone: +1-212-355-4449

    Web Site: www.potashcorp.com

For further information, please contact: Investors: Denita Stann, Senior Director, Investor Relations, Phone: +1-847-849-4277, Email: ir at potashcorp.com; Media: Bill Johnson, Director, Public Affairs, Phone: +1-306-933-8849, Email: pr at potashcorp.com; Eric Brielmann / Jamie Moser / Andrew Siegel, Joele Frank, Wilkinson Brimmer Katcher, Phone: +1-212-355-4449