Document:

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                                                                  Exhibit 10(aa)

                    POTASH CORPORATION OF SASKATCHEWAN INC.
                  STOCK OPTION PLAN -- OFFICERS AND EMPLOYEES

1.   PURPOSE OF PLAN

     Potash Corporation of Saskatchewan Inc. (the "Corporation") by resolution
     of its Board of Directors (the "Board") has established this Plan to
     encourage officers and employees of the Corporation and its subsidiaries to
     promote the growth and profitability of the Corporation by providing them
     with the opportunity through options to acquire Common Shares of the
     Corporation ("Common Shares").

2.   ADMINISTRATION

     This Plan shall be administered by the Board.

3.   GRANT OF OPTIONS

     From time to time the Board may designate individual officers and employees
     of the Corporation and its subsidiaries eligible to be granted options to
     purchase Common Shares and the number of Common Shares which each such
     person will be granted an option to purchase; provided that the aggregate
     number of Common Shares subject to such options may not exceed the number
     provided for in paragraph 4 of this Plan.

4.   SHARES SUBJECT TO OPTION

     The aggregate number of Common Shares issuable after February 3, 1998
     pursuant to options under this Plan may not exceed 6,926,125 shares. The
     number of Common Shares issuable pursuant to options under this Plan shall
     be subject to adjustment under paragraphs 8 and 9.

     The aggregate number of Common Shares in respect of which options have been
     granted to any one person and which remain outstanding shall not at any
     time exceed 5% of the number of issued and outstanding Common Shares (on a
     non-diluted basis) at that time.

     If any option granted under this Plan, or any portion thereof, expires or
     terminates for any reason without having been exercised in full, the Common
     Shares with respect to which such option has not been exercised shall again
     be available for further options under this Plan.

5.   OPTION PRICE

     The option price under this Plan to any optionee shall be fixed by the
     Board when the option is granted and shall be not less than the fair market
     value of the Common Shares at such time which, for optionees resident in
     the United States and any other optionees designated by the Board, shall be
     deemed to be the closing price per share of the Common Shares on the New
     York Stock Exchange on the last trading day immediately preceding the day
     the option is granted and, for all other optionees, shall be deemed to be
     the closing price per share of the Common Shares on The Toronto Stock
     Exchange on the last trading day immediately preceding the day the option
     is granted; provided that, in either case, if the Common Shares did not
     trade on such exchange on such day the option price shall be the closing
     price per share on such exchange on the last day on which the Common Shares
     traded on such exchange prior to the day the option is granted.

6.   TERMS OF OPTION

     The period during which an option is exercisable may not exceed 10 years
     from the date the option is granted, and the option agreement may contain
     provisions limiting the number of Common Shares with
<PAGE>   2

     respect to which the option may be exercised in any one year. Each option
     agreement shall contain provisions to the effect that:

     a.    if the employment of an optionee as an officer or employee of the
           Corporation or a subsidiary terminates, by reason of his or her
           death, or if an optionee who is a retiree pursuant to clause b below
           dies, the legal personal representatives of the optionee will be
           entitled to exercise any unexercised options, including such options
           that may vest after the date of death, during the period ending at
           the end of the twelfth calendar month following the calendar month in
           which the optionee dies, failing which exercise the options
           terminate;

     b.    subject to the terms of clause a above, if the employment of an
           optionee as an officer or employee of the Corporation or a subsidiary
           terminates, by reason of retirement in accordance with the then
           prevailing retirement policy of the Corporation or subsidiary, the
           optionee will be entitled to exercise any unexercised options,
           including such options as may vest after the date of retirement,
           until the expiry date of such options or the date on which such
           options are otherwise terminated in accordance with the provisions of
           this Plan, failing which exercise the options terminate.
           Notwithstanding the foregoing, the Board may, at the time of grant,
           prescribe such shorter period of time for exercise following
           retirement as it deems appropriate;

     c.    if the employment of an optionee as an officer or employee of the
           Corporation or a subsidiary terminates, for any reason other than as
           provided in the preceding clauses a or b, the optionee will be
           entitled to exercise any unexercised options, to the extent
           exercisable at the date of such event, during the period ending at
           the end of the calendar month immediately following the calendar
           month in which the event occurs, failing which exercise the options
           terminate.

           For greater certainty and for these purposes, an optionee's
           employment with the Corporation or a subsidiary shall be considered
           to have terminated effective on the last day of the optionee's actual
           and active employment with the Corporation or subsidiary whether such
           day is selected by agreement with the optionee or unilaterally by the
           Corporation or subsidiary and whether with or without advance notice
           to the optionee. For the avoidance of doubt, no period of notice that
           is given or ought to have been given under applicable law in respect
           of such termination of employment will be utilized in determining an
           optionee's entitlement under the Plan; and

     d.    each option is personal to the optionee and is not assignable, except
           (i) as provided in the preceding clause a, and (ii) at the election
           of the Board, an option may be assignable to the spouse, children and
           grandchildren of the original optionee and to a trust, partnership or
           limited liability company, the entire beneficial interest of which is
           held by one or more of the foregoing.

    Nothing contained in the preceding clauses a, b, or c shall extend the
    period during which an option may be exercised beyond its stipulated expiry
    date or the date on which it is otherwise terminated in accordance with the
    provisions of this Plan.

    If an option is assigned pursuant to the preceding subclause (ii) of clause
    d, the references in the preceding clauses a, b and c to the termination of
    employment or death of an optionee shall not relate to the assignee of an
    option but shall relate to the original optionee. In the event of such
    assignment, legal personal representatives of the original optionee shall
    not be entitled to exercise the assigned option, but the assignee of the
    option or the legal personal representatives of the assignee may exercise
    the option during the applicable specified period.

7.  EXERCISE OF OPTIONS

    Subject to the provisions of this Plan, an option may be exercised from time
    to time by delivering to the Corporation at its registered office a written
    notice of exercise specifying the number of shares with respect to which the
    option is being exercised and accompanied by payment in cash or certified
    cheque in full of the purchase price of the shares then being purchased.
<PAGE>   3

8.  ADJUSTMENTS

    Appropriate adjustments to the authorized limits set forth in paragraph 4,
    in the number, class and/or type of shares optioned and in the option price
    per share, both as to options granted or to be granted, may be made by the
    Board in its discretion to give effect to adjustments in the number of
    Common Shares which result from subdivisions, consolidations or
    reclassifications of the Common Shares, the payment of share dividends by
    the Corporation, the reconstruction, reorganization or recapitalization of
    the Corporation or other relevant changes in the capital of the Corporation.
    If the Corporation sells all or substantially all of its assets as an
    entirety or substantially as an entirety, options under this Plan may be
    exercised, in whole or in part, at any time up to and including (but not
    after) a date 30 days following the date of completion of such sales or
    prior to the close of business on the date the option expires, whichever is
    earlier.

9.  MERGERS

    If the Corporation proposes to amalgamate or merge with another body
    corporate, the Corporation shall give written notice thereof to optionees in
    sufficient time to enable them to exercise outstanding options, to the
    extent they are otherwise exercisable by their terms, prior to the effective
    date of such amalgamation or merger if they so elect. The Corporation shall
    use its best efforts to provide for the reservation and issuance by the
    amalgamated or continuing corporation of an appropriate number of shares,
    with appropriate adjustments, so as to give effect to the continuance of the
    options to the extent reasonably practicable. In the event that the Board
    determines in good faith that such continuance is not in the circumstances
    practicable, it may upon 30 days' notice to optionees terminate the options.

10. CHANGE OF CONTROL

    If a "change of control" of the Corporation occurs, each then outstanding
    option granted under this Plan may be exercised, in whole or in part, even
    if such option is not otherwise exercisable by its terms. For purposes of
    this paragraph 10, a change of control of the Corporation shall be deemed to
    have occurred if:

     a.    within any period of two consecutive years, individuals who at the
           beginning of such period constituted the Board and any new directors
           whose appointment by the Board or nomination for election by
           shareholders of the Corporation was approved by a vote of at least a
           majority of the directors then still in office who either were
           directors at the beginning of the period or whose appointment or
           nomination for election was previously so approved, cease for any
           reason to constitute a majority of the Board;

     b.    there occurs an amalgamation, merger, consolidation, wind-up,
           reorganization or restructuring of the Corporation with or into any
           other entity, or a similar event or series of such events, other than
           any such event or series of events which results in securities of the
           surviving or consolidated corporation representing 50% or more of the
           combined voting power of the surviving or consolidated corporation's
           then outstanding securities entitled to vote in the election of
           directors of the surviving or consolidated corporation being
           beneficially owned, directly or indirectly, by the persons who were
           the holders of the Corporation's outstanding securities entitled to
           vote in the election of directors of the Corporation prior to such
           event or series of events in substantially the same proportions as
           their ownership immediately prior to such event of the Corporation's
           then outstanding securities entitled to vote in the election of
           directors of the Corporation;

     c.    50% or more of the fixed assets (based on book value as shown on the
           most recent available audited annual or unaudited quarterly
           consolidated financial statements) of the Corporation are sold or
           otherwise disposed of (by liquidation, dissolution, dividend or
           otherwise) in one transaction or series of transactions within any
           twelve month period;

     d.    any party, including persons acting jointly or in concert with that
           party, becomes (through a take-over bid or otherwise) the beneficial
           owner, directly or indirectly, of securities of the Corporation
           representing 20% or more of the combined voting power of the
           Corporation's then outstanding
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           securities entitled to vote in the election of directors of the
           Corporation, unless in any particular situation the Board determines
           in advance of such event that such event shall not constitute a
           change of control; or

     e.    the Board approves and/or recommends that shareholders accept,
           approve or adopt any transaction that would constitute a change of
           control under clause b, c or d above.

11. AMENDMENT OR DISCONTINUANCE OF THIS PLAN

    The Board may amend or discontinue the Plan at any time but, subject to
    paragraphs 8, 9, and 10, no such amendment may increase the aggregate
    maximum number of shares that may be subject to option under this Plan,
    change the manner of determining the minimum option price, extend the option
    period under any option beyond 10 years or, without the consent of the
    holder of the option, alter or impair any option previously granted to an
    optionee under this Plan. Amendments to the Plan require pre-clearance of
    The Toronto Stock Exchange.

12. EVIDENCE OF OPTIONS

    Each option granted under this Plan shall be embodied in a written option
    agreement between the Corporation and the optionee which shall give effect
    to the provisions of this Plan.<PAGE>   1

                                                                  Exhibit 10(ii)

                    POTASH CORPORATION OF SASKATCHEWAN INC.
                              ("THE CORPORATION")

                             DIRECTORS' RESOLUTION

WHEREAS the bylaws of the Corporation require the Corporation to indemnify
directors and officers of the Corporation and each person who acts at the
Corporation's request as a director or officer of a body corporate of which the
Corporation is a shareholder or creditor against all costs reasonably incurred
by him or her in respect of any civil, criminal or administrative proceeding to
which he or she is made party by reason of being or having been a director or
officer of the Corporation or such body corporate;

AND WHEREAS such indemnification is permitted under the laws of the Province of
Saskatchewan;

AND WHEREAS the laws of the Province of Saskatchewan permit each director of the
Corporation to vote on a resolution approving a contract to which he or she is a
party if the contract is one for indemnification under section 119 of The
Business Corporation's Act;

AND WHEREAS it is considered to be in the best interests of the Corporation that
such contracts of indemnification be entered into, as appropriate, with
officers, former officers, directors and former directors of the Corporation and
with each person who acts or has acted at the Corporation's request as a
director or officer of a body corporate of which the Corporation is or was a
shareholder or creditor;

THEREFORE, BE IT RESOLVED THAT:

The Senior Vice President, General Counsel and Secretary or in his absence any
officer or director of the Corporation be and is hereby authorized on a
continuing basis to enter into a contract of indemnity, substantially in the
form set out in SCHEDULE I to this resolution, with each officer and director of
the Corporation and with each person who acts or has acted at the Corporation's
request as a director or officer of a body corporate of which the Corporation is
or was a shareholder or creditor, as such directors or officers may be elected
or appointed from time-to-time.
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                                                                      SCHEDULE I

                          AGREEMENT OF INDEMNIFICATION

THIS AGREEMENT made the    --   day of 200 -- .

BETWEEN:
            POTASH CORPORATION OF SASKATCHEWAN INC. (a corporation
            incorporated under The Business Corporations Act (Saskatchewan),
                                                            (the "Corporation");

                                - and -

            (INDEMNITEE'S NAME) of the City of ________, in the  ______________,
                                                             (the "Indemnitee").

WHEREAS it is essential to the Corporation and to the bodies corporate of which
the Corporation is a shareholder or creditor (collectively the "Included
Corporations") to retain and attract as directors and officers the most capable
persons available;

AND WHEREAS, for that purpose, it is the policy of the Corporation to indemnify
its directors and officers and the persons who, at the Corporation's request,
act as directors or officers of bodies corporate in which the Corporation is a
shareholder or creditor (collectively the "Eligible Indemnitees") as permitted
by law;

AND WHEREAS, the bylaws of the Corporation require the Corporation to indemnify
its Eligible Indemnitees whenever required or permitted by law;

AND WHEREAS the Corporation has requested the Indemnitee to act or to continue
to act as a director or officer, or both of one or more or the Included
Corporations;

AND WHEREAS the Indemnitee has agreed to act or to continue to act as a director
or officer, or both, of one or more of the Included Corporations upon the
condition that the Corporation executes and delivers this agreement of
indemnification;

NOW, THEREFORE, THIS AGREEMENT WITNESSETH that in consideration of the premises
and the mutual covenants herein contained and for good and valuable
consideration, the receipt of which is hereby acknowledged by both parties, the
Corporation and Indemnitee agree as follows:

1.   AGREEMENT TO SERVE: The Indemnitee agrees to act or to continue to act as a
     director an/or officer of one or more or the Included Corporations for so
     long as he or she is duly elected or appointed or until such time as he or
     she ceases to be a director or officer, whether by resignation in writing
     or otherwise.

2.   INDEMNITY RIGHT: To the extent permitted under applicable law, and subject
     to the further terms and conditions of this agreement, the Corporation
     hereby agrees to indemnify the Indemnitee against all costs, charges and
     expenses, including any amount paid to settle an action or satisfy a
     judgment, reasonably incurred by the Indemnitee in respect of any civil,
     criminal or administrative action or proceeding to which the Indemnitee is
     made a party by reason of being or having been a director or officer, or
     both, of one or more of the Included Corporations.

3.  SCOPE: The agreement extends to all acts, omissions, circumstances and
    events, whether occurring before or after the date of this agreement.

4.   CONDITIONS PRECEDENT:

        a)  NOTICE: The indemnitee shall, as soon as reasonably practicable
            after becoming aware of any claim, demand, action or proceeding
            which may give rise to indemnification hereunder, give written
            notice to the Corporation, directed to its corporate secretary,
            provided however, that failure to give notice in a timely fashion
            shall not disentitle the Indemnitee to the right to indemnity
            hereunder except to the extent the Corporation suffers actual
            prejudice by reason of the delay.
<PAGE>   3

        b)  GENERAL CONDITIONS: Notwithstanding anything herein contained, and
            for greater certainty, the indemnity provided by Section 2 is only
            available to the Indemnitee if:

            i)    the Indemnitee acted honestly and in good faith with a view to
                  the best interests of the Included Corporations; and

            ii)   in the case of a criminal or administrative action or
                  proceeding that is enforced by a monetary penalty, the
                  Indemnitee had reasonable grounds for believing that the
                  conduct in question was lawful; and

            iii)  in respect of an action by or on behalf of an Included
                  Corporation to procure a judgment in its favour, to which the
                  Indemnitee is made a party by reason of being or having been a
                  director or officer of the Included Corporation, a court of
                  competent jurisdiction gives its approval to the Included
                  Corporation to indemnify the Indemnitee.

        c)  DEFENCE COSTS: The Corporation shall not be liable for any defence
            costs (including without limitation, any costs, charges and expenses
            to investigate, defend, or monitor any action or proceeding)
            incurred without its prior express consent, which consent shall not
            be unreasonably withheld. In considering the reasonableness of any
            request by the Indemnitee that the Corporation consent to the
            incurring of defence costs, the Corporation may consider, without
            limitation, the proposed choice of defence counsel, the terms of
            engagement or proposed counsel and the extent to which the defence
            costs may be controlled or limited through common efforts, including
            the employment of common counsel, with other directors and officers
            of the Included Corporation, without the creation of actual or
            perceived conflicts of interest.

        d)  SETTLEMENTS: The Corporation shall not be liable for any costs,
            charges, or expenses incurred in connection with any settlement in
            respect of any claim, demand, action or proceeding against the
            Indemnitee which has been entered into without the prior express
            consent of the Corporation. For greater clarity, and without
            limiting in any way the generality of the foregoing, in the event
            that the Indemnitee enters into any such settlement without the
            prior express consent of the Corporation, the Corporation shall not
            be responsible for indemnifying the Indemnitee for any compensation
            or other payment to be made under the settlement or for costs of
            negotiating or implementing the settlement and the Indemnitee shall
            not seek indemnity from the Corporation in respect of any other
            costs, charges or expenses in association with such settlement.

        e)  OTHER INDEMNIFICATION: The parties hereto contemplate that insurance
            may be purchased that my provide indemnification or reimbursement to
            the Indemnitee for costs, charges and/or expenses in some or all of
            the circumstances described in Section 2 hereof. It is a condition
            of this indemnity that the Corporation is only liable to indemnify
            the Indemnitee if, and to the extent that, the Indemnitee has not in
            fact received from any other person, indemnification or
            reimbursement for the costs, charges and expenses in respect of
            which indemnification is ought by the Indemnitee from the
            Corporation, including by reason of or through any policy of
            insurance.

     5. FURTHER EXCEPTIONS: Notwithstanding anything herein contained, the
        indemnity proved by Section 2 shall not be applicable to or in respect
        of any claim arising from:

        a)   any act, omission, circumstance or event, in respect of which it is
             proven that the Indemnitee has improperly profited by the conduct
             which is the subject of the claim, demand, action or proceeding,
             whether by trading activities contrary to securities laws or
             otherwise;

        b)   failure of the Indemnitee to act in accordance with specific and
             lawful instructions or directions of the board of directors, or an
             officer who is entitled to provide instruction or directions to the
             Indemnitee, of the Included Corporation.
<PAGE>   4

     6.   APPROVALS: Where any indemnification sought pursuant to Section 2
          hereof is, under applicable law, subject to or conditional upon the
          approval or consent of any court or of any governmental body or
          regulatory authority, the Corporation agrees to make or cause to be
          made all necessary applications and to use its reasonable best efforts
          to obtain or assist in obtaining or facilitating the obtaining of such
          approval or consent.

     7.   RIGHT TO RESIGN AND SURVIVAL: Nothing in this agreement shall prevent
          the Indemnitee from resigning as a director or officer, or both, of
          the Corporation or any other body corporate at any time. This
          agreement shall survive any such resignation or any other circumstance
          by reason of which the Indemnitee shall cease to be a director or
          officer of the Corporation or any other body corporate.

     8.   SETTLEMENT FOR CORPORATION: Subject to the consent of the Indemnitee,
          the Corporation may enter into a settlement or other agreement to
          compromise a claim, demand, action or proceeding which has given rise
          to a notice of claim for indemnity hereunder.

          If the Indemnitee refuses to give consent to the terms of a proposed
          settlement or compromise which is otherwise acceptable to the
          Corporation, any amount awarded against the Indemnitee in excess of
          the amount for which settlement or compromise could have been made by
          the Corporation shall not be recoverable under this agreement, it
          being further agreed by the parties that in such event the Corporation
          shall only be responsible for costs, charges and expenses up to the
          time at which settlement could have been made.

     9.   ADVANCE PAYMENT OF DEFENCE COSTS: Except as otherwise expressly
          provided herein, it is contemplated by the parties that in the event
          the Indemnitee is not receiving indemnification from any other source
          during the course of any action or proceeding for which indemnity is
          available pursuant to this agreement, the Corporation will advance and
          pay all costs, charges and expenses associated with the defence and
          appeal of the claim, demand, action or proceeding as they are
          incurred, provided however that if:

          a)   it is subsequently is demonstrated that the Indemnitee is not
               entitled to indemnity for any reason the amounts so advanced and
               paid by the Corporation shall be repaid by the Indemnitee to the
               Corporation forthwith upon request;

          b)   The Indemnitee subsequently receives indemnification or
               reimbursement for all or part of any costs, charges or expenses
               from a source or sources other than the Corporation, the amounts
               so advanced and paid by the Corporation shall be repaid by the
               Indemnitee to the Corporation forthwith upon request, to the
               extent that the Indemnitee receives indemnification or
               reimbursement from such other source or sources.

     10.  SUBROGATION: To the extent permitted by law, the Corporation shall be
          subrogated to all rights which the Indemnitee may have under all
          policies of insurance or other contracts pursuant to which the
          Indemnitee may be entitled to reimbursement of, or indemnification in
          respect of, all or any part of the costs, charges and expenses which
          are borne by the Corporation pursuant to this agreement.

     11.  PROPER LAW AND ATTORNMENT: This agreement shall be construed in
          accordance with an governed by the laws of the Province of
          Saskatchewan and the parties hereto attorn to the jurisdiction of the
          courts of Saskatchewan in respect of any proceedings arising out of
          this agreement.

     12.  SEVERABILITY: Each section and each provision within each section, of
          this agreement is severable, the one from the other, and if for any
          reason any section or provision of this agreement is not enforceable
          or is otherwise invalid at law, or would render invalid or
          unenforceable any policy of insurance purchased by the Corporation on
          behalf of or for the benefit of either the Corporation or the
          Indemnitee, the same shall be severed from the remainder of the
          agreement and the remainder of this agreement shall nonetheless be
          given full force and effect in accordance with its terms.
<PAGE>   5

     13.  FURTHER RESPONSIBILITIES AND ASSURANCES: The Indemnitee:

          a)   shall attend diligently to, and assist in the conduct of, the
               defence of any claim, demand, action or proceeding, shall assist
               in enforcing any right of contribution or indemnity against any
               person or organization and shall attend hearings and trials and
               assist in securing and giving of evidence and obtaining the
               attendance of witnesses;

          b)   shall not voluntarily make any payment, assume any obligation or
               admit any liability in respect of any claim, demand, action or
               proceeding without the prior express consent of the Corporation;
               and

          c)   shall execute such further assurances and documents, give such
               consents and perform such further acts as the Corporation may
               reasonable request in order that the Corporation may enjoy the
               full benefits of this agreement in accordance with its terms and
               for that purpose shall enter into such assignments, powers of
               attorney and other documents as may be reasonably required in the
               circumstances.

     14.  AMENDMENT: This agreement may be amended only by written instrument
          executed by the Corporation and the Indemnitee.

     15.  ENUREMENT AND SUCCESSORS: This agreement is irrevocable and enures to,
          and is binding upon, the parties hereto and their respective heirs,
          successors, representatives and assigns.

IN WITNESS WHEREOF the Corporation and the Indemnitee have executed this
Agreement as of the day and year first written above.

                                     POTASH CORPORATION OF SASKATCHEWAN INC.

                                     By:
                                       -----------------------------------------

                                     By:
                                       -----------------------------------------

<TABLE>
<S>                                              <C>
SIGNED in the presence of

----------------------------------     -----------------------------------------
Witness                                          (Indemnitee Name)
</TABLE>

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