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                                                                   EXHIBIT 10.31


                            STOCK PURCHASE AGREEMENT

     THIS STOCK PURCHASE AGREEMENT (the "Agreement"), dated as of the date of
acceptance set forth below, is entered into by and between SPSS INC., a Delaware
corporation, with headquarters located at 233 South Wacker Drive, Chicago,
Illinois 60606 ("SPSS"), and SIEBEL SYSTEMS, INC., a Delaware corporation, with
headquarters located at 2207 Bridgepointe Parkway, San Mateo, California 94404
(the "Buyer").

                              W I T N E S S E T H:

     WHEREAS, SPSS and the Buyer are executing and delivering this Agreement in
accordance with and in reliance upon an exemption from securities registration
afforded, inter alia, by Rule 506 under Regulation D ("Regulation D") as
promulgated by the United States Securities and Exchange Commission (the "SEC")
under the Securities Act of 1933, as amended (the "1933 Act" or the "Act"),
and/or Section 4(2) of the 1933 Act; and

     WHEREAS, the Buyer wishes to purchase, upon the terms and subject to the
conditions of this Agreement, such number of newly issued, unregistered shares
of common stock, $0.01 par value per share (the "Common Stock") of SPSS as more
fully described herein, subject to acceptance of this Agreement by SPSS;

     NOW THEREFORE, in consideration of the premises and the mutual covenants
contained herein and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties agree as follows:

     1.   AGREEMENT TO PURCHASE; PURCHASE PRICE; CLOSING.

     a.   AGREEMENT TO PURCHASE; PURCHASE PRICE. The undersigned shall purchase
from SPSS on the Closing date that number of shares of SPSS Common Stock (the
"Shares") calculable based upon a price per share equal to ninety-five percent
(95%) of the average of the closing price of SPSS Common Stock, as quoted on the
NASDAQ National Market ("NASDAQ") for the ten (10) trading days following SPSS's
release of its earnings for the period ending June 30, 2001, which price is
$16.65 (the "Per Share Purchase Price"), and an aggregate purchase price equal
to FIVE MILLION AND NO/100 DOLLARS ($5,000,000) (subject to adjustment to
prevent the issuance of fractional Shares) (the "Purchase Price").
Notwithstanding anything to the contrary contained herein, fractional Shares
shall not be issued. In lieu of fractional shares, the Purchase Price shall be
adjusted such that only whole Shares shall be issued hereunder. Payment of the
Purchase Price will be made by Buyer by wiring immediately available funds in
United States dollars to an account designated by SPSS.

     b.   CLOSING. The Closing of the purchase, sale and issuance of the Shares
shall take place at the principal office of SPSS, 233 South Wacker Drive,
Chicago, Illinois 60606 on or before September 28, 2001 or at such other time
and date as the parties hereto may agree (the "Closing"). At the Closing, SPSS
shall deliver to the Buyer a certificate or certificates in the Buyer's name for
the number of Shares set forth on the signature page hereto, against receipt
from the Buyer of the Purchase Price.


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     2.   BUYER REPRESENTATIONS AND WARRANTIES.

     The Buyer represents and warrants to, and covenants and agrees with, SPSS
as follows:

     a.   Without limiting Buyer's right to sell the Common Stock pursuant to
the Registration Statement (as defined below), the Buyer is purchasing the
Shares for its own account for investment only and not with a view towards the
resale or distribution of any part thereof and not with a view to or for sale in
connection with any distribution thereof.

     b.   The Buyer is (i) an "accredited investor" as that term is defined in
Rule 501 of Regulation D as presently in effect, (ii) experienced in making
investments of the kind described in this Agreement and the related documents,
(iii) able, by reason of the business and financial experience of its officers
(if an entity) and/or professional advisors (who are not affiliated with or
compensated in any way by SPSS or any of its affiliates or selling agents), to
protect its own interests in connection with the transactions described in this
Agreement, and the related documents, and (iv) able to afford the entire loss of
its investment in the Shares.

     c.   The Buyer understands that the Shares have not been registered under
the 1933 Act, or any applicable state securities laws. Therefore, the Buyer
shall not sell or offer to sell the Shares except pursuant to registration of
the Shares under the 1933 Act or an exemption from registration requirements of
United States federal and state securities laws and in compliance with all
applicable state securities laws.

     d.   The Buyer understands that the Shares are being offered and sold to it
in reliance on specific exemptions from the registration requirements of United
States federal and state securities laws and that SPSS is relying upon the truth
and accuracy of, and the Buyer's compliance with, the representations,
warranties, agreements, acknowledgments and understandings of the Buyer set
forth herein in order to determine the availability of such exemptions and the
eligibility of the Buyer to acquire the Shares.

     e.   The Buyer and its advisors have been furnished with all materials
relating to the business, finances and operations of SPSS and materials relating
to the offer and sale of the Shares which have been requested by the Buyer. The
Buyer and its advisors have been afforded the opportunity to ask questions of
SPSS and have received complete and satisfactory answers to any such inquiries.

     f.   The Buyer understands that no United States federal or state agency or
any other government or governmental agency has passed on or made any
recommendation or endorsement of the Shares.

     g.   This Agreement has been duly and validly authorized, executed and
delivered on behalf of the Buyer and is a valid and binding agreement of the
Buyer enforceable in accordance with its terms, subject as to enforceability to
general principles of equity and to bankruptcy, insolvency, moratorium and other
similar laws affecting the enforcement of creditors' rights generally.


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     3.   SPSS REPRESENTATIONS AND WARRANTIES.

     SPSS represents and warrants to the Buyer that:

     a.   SPSS STATUS.

          (i)   SPSS is a corporation duly organized, validly existing and in
                good standing under the laws of the State of Delaware, and has
                the requisite power (corporate and other) and authority to own
                its properties, to carry on its business as now being conducted
                and to perform its obligations under any contract filed as an
                exhibit to any SPSS SEC Documents (as defined below).

          (ii)  SPSS is qualified to do business as a foreign corporation, and
                is in good standing, in each jurisdiction in which the nature of
                its business and of its properties makes such qualification
                necessary, except where the failure to be so qualified would not
                have a material adverse effect on SPSS's business, condition
                (financial or otherwise), assets, liabilities or operations.

     b.   SEC FILINGS; FINANCIAL STATEMENTS.

          (i)   SPSS has made available to the Buyer accurate and complete
                copies of each report, registration statement and definitive
                proxy statement filed by SPSS with the SEC since August 4, 1993
                (the "SPSS SEC Documents"). As of the time it was filed with the
                SEC (or, if amended or superseded by a filing prior to the date
                of this Agreement, then on the date of such filing): (a) each of
                the SPSS SEC Documents complied in all material respects with
                the applicable requirements of the 1933 Act or the 1934 Act (as
                defined herein), as the case may be; and (b) none of the SPSS
                SEC Documents contained any untrue statement of a material fact
                or omitted to state a material fact required to be stated
                therein or necessary in order to make the statements therein, in
                light of the circumstances under which they were made, not
                misleading. There are no contracts or other documents of SPSS
                that are required to be filed as exhibits to the SPSS SEC
                Documents which have not been filed.

          (ii)  The consolidated financial statements contained in the SPSS SEC
                Documents: (a) complied as to form in all material respects with
                the published rules and regulations of the SEC applicable
                thereto; (b) were prepared in accordance with generally accepted
                accounting principles applied on a consistent basis throughout
                the periods covered, except as may be indicated in the notes to
                such financial statements and (in the case of unaudited
                statements) as permitted by Form 10-Q promulgated by the SEC,
                and except that unaudited financial statements may not contain
                footnotes and are subject to year-end audit adjustments (which
                are not reasonably expected to be, individually or in the
                aggregate, material in


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                amount); and (c) fairly present the consolidated financial
                position of SPSS and its subsidiaries as of the respective dates
                thereof and the consolidated results of operations of SPSS and
                its subsidiaries for the periods covered thereby.

          (iii) Except for the liabilities included or reserved for in the
                audited balance sheet of the Company for the year ended December
                31, 2000, included in the Form 10-K or the unaudited
                consolidated balance sheet of SPSS included in its Quarterly
                Report on Form 10-Q (the "Form 10-Q") for the quarter ended June
                30, 2001 (the "Balance Sheet"), each as filed with the SEC, SPSS
                did not have, and since such date it has not incurred,
                liabilities or any other obligations whatsoever that are
                material (individually or in the aggregate) to SPSS, except
                current liabilities incurred in the ordinary course of business
                consistent with past practice subsequent to June 30, 2001.

     c.   AUTHORIZED SHARES. The Shares have been duly authorized and, when
issued to Buyer, will be duly and validly issued, fully paid and non-assessable.

     d.   AUTHORITY; BINDING AGREEMENT. SPSS has the absolute and unrestricted
right, power and authority to enter into and perform its obligations under this
Agreement, and the execution, delivery and performance by SPSS of this Agreement
and the transactions contemplated hereby (including the contemplated issuance of
the Shares), have been duly and validly authorized by SPSS, this Agreement has
been duly executed and delivered by SPSS. No vote of SPSS's stockholders is
needed to approve the sale and issuance of the Shares to the Buyer. This
Agreement, when executed and delivered by SPSS, will be a legal, valid and
binding agreement of SPSS, enforceable against it in accordance with its terms,
subject as to enforceability to general principles of equity and to bankruptcy,
insolvency, moratorium, and other similar laws affecting the enforcement of
creditors' rights generally.

     e.   NON-CONTRAVENTION. The execution and delivery of this Agreement by
SPSS, the issuance of the Shares, and the consummation by SPSS of the
transactions contemplated by this Agreement do not and will not conflict with or
result in a breach by SPSS of any of the terms or provisions of, or constitute a
default under (i) the articles of incorporation or by-laws of SPSS, (ii) any
indenture, mortgage, deed of trust, or other material agreement or instrument to
which SPSS is a party or by which it or any of its properties or assets are
bound, (iii) to its knowledge, any existing applicable law, rule, or regulation
or any applicable decree or judgment, or (iv) to its knowledge, order of any
court, United States federal or state regulatory body, administrative agency, or
other governmental body having jurisdiction over SPSS or any of its properties
or assets, except any such conflict, breach or default which would not have a
material adverse effect on the transactions contemplated herein.

     f.   APPROVALS. No authorization, approval or consent of any court,
governmental body, regulatory agency, self-regulatory organization, stock
exchange or market or third party is required to be obtained by SPSS for the
issuance and sale of the Shares to the Buyer as contemplated by this Agreement,
except such authorizations, approvals and consents that have been obtained.


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     g.   OFFERING VALID. Assuming the accuracy of the representations and
warranties of the Buyer contained in Section 2 hereof, the offer, sale and
issuance of the Shares will be exempt from the registration requirements of the
Securities Act and will have been registered or qualified (or are exempt from
registration and qualification) under the registration, permit or qualification
requirements of all applicable state securities laws. Neither SPSS nor any agent
on its behalf has solicited or will solicit any offers to sell or has offered to
sell or will offer to sell all or any part of the Shares to any person or
persons or take any other action so as to bring the sale of such Shares by SPSS
within the registration provisions of the 1933 Act or any state securities laws.

     h.   ABSENCE OF CHANGES. From June 30, 2001 to the date of this Agreement,
there has not been any material adverse change in SPSS's business, condition
(financial or otherwise), assets, liabilities or operations and SPSS has carried
on its business in the ordinary course consistent with past practices.

     i.   LEGAL PROCEEDINGS; ORDERS. There is no pending Legal Proceeding and to
the best of SPSS's knowledge, no person or entity has threatened to commence any
Legal Proceeding (i) against SPSS that could reasonably be expected to have a
material adverse effect on SPSS's business, condition (financial or otherwise),
assets, liabilities or operations (other than any actual or threatened Legal
Proceeding that has been previously disclosed by SPSS in any of the SPSS SEC
Documents); or (ii) that challenges, or that may have the effect of preventing,
delaying, making illegal or otherwise interfering with, the sale and issuance of
the Shares of the Buyer. To the best of SPSS's knowledge, no event has occurred,
and no claim, dispute or other condition or circumstance exists, that will, or
that could reasonably be expected to, give rise to or serve as a basis for the
commencement of any such Legal Proceeding.

     j.   REGISTRATION STATEMENT ELIGIBILITY. SPSS is eligible to use a
Registration Statement on Form S-3.

     4.   SECURITIES MATTERS

     a.   REGISTRATION OF SPSS COMMON STOCK.

          (i)   SPSS shall prepare and file with the SEC a registration
                statement on Form S-3 (together with all amendments and
                supplements to any such registration statement, including
                post-effective amendments, and all material incorporated by
                reference or deemed to be incorporated by reference in such
                registration statement, the "Registration Statement") under the
                1933 Act, and the rules and regulations promulgated thereunder,
                for the registration (the "Registration") of the offering of the
                Shares for the account of the Buyer. SPSS shall take such steps
                as are reasonably required to register such SPSS Common Stock
                for sale on a delayed or continuous basis under Rule 415 of the
                1933 Act and, provided that Form S-3 shall be available to SPSS
                for the Registration, to keep such Registration Statement
                continuously effective, current and available for use by the
                Buyer until such time as all of the Shares have been sold by the
                Buyer (the "Trading Period").


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          (ii)  The Buyer shall cooperate with SPSS in connection with the
                Registration and shall provide such information and execute such
                documents as SPSS shall reasonably request in connection with
                the Registration.

          (iii) SPSS shall permit the Buyer, at Buyer's cost and expense (except
                as otherwise specifically provided in Section 4(c), to review
                and have a reasonable opportunity to comment on the Registration
                Statement and all amendments and supplements thereto at least
                three (3) business days prior to their filing with the SEC and
                shall not file any such document to which Buyer reasonably
                objects.

          (iv)  Subject to Buyer's rights under clause (iii) above, SPSS hereby
                covenants and agrees that it will file the Registration
                Statement with the SEC no more that eight (8) business days
                following the Closing and, if the Registration Statement is
                reviewed by the SEC and the SEC provides comment with respect
                thereto ("SEC Comment"), will A) promptly provide to Buyer 1) a
                copy of any written SEC Comment with the date on which SPSS
                received SEC Comment, 2) a written summary of any SEC Comment
                received by SPSS in verbal, non-written format from the SEC and
                the date on which SPSS received SEC Comment, B) prepare and file
                a response, including, if necessary, an amendment to the
                Registration Statement, no more than eight (8) business days
                following the date on which SPSS receives such comments, and C)
                provide to Buyer a copy of any response by SPSS to a SEC Comment
                and the date on which SPSS delivered the response to the SEC
                Comment to the SEC.

          (v)   SPSS hereby covenants and agrees that it will file a request for
                acceleration pursuant to Rule 461 no more than five (5) business
                days following the date on which it is advised by the SEC that
                the SEC does not intend to comment or further comment, as the
                case may be, on the Registration Statement.

          (vi)  In the event that SPSS shall fail to satisfy its obligations
                under either clause (iii) or (iv) above, notwithstanding SPSS's
                receipt of Buyer's written approval of the contents of the
                Registration Statement or any applicable amendment or supplement
                thereto within three (3) business days after the date on which
                SPSS has delivered the Registration == Statement or any
                amendment or supplement thereto to Buyer for its review pursuant
                to clause (iii) above, SPSS shall pay Siebel an amount equal to
                $2,500 for each full business day during which such failure is
                continuing, provided, however, that SPSS's maximum liability for
                all such failures shall not exceed $100,000. Payment of
                penalties under this subsection 4(a) shall be made by SPSS to
                Buyer on the fifth (5th) day of each calendar month following
                the date on which the penalty occurs for the amount of penalties
                owed for the prior calendar month.


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          (vii) SPSS shall not grant to any holder of shares of SPSS Common
                Stock registration rights that interfere with the rights of the
                Buyer and the obligations of SPSS under this Section 4.

     b.   SALES OF SPSS COMMON STOCK BY THE BUYER. If at any time prior to the
effectiveness of the Registration Statement the Buyer elects to sell all or any
portion of the Shares, the Buyer shall conduct such sales only through
registered securities brokers ("brokers").

     c.   REGISTRATION EXPENSES. SPSS shall be responsible for and shall pay all
fees, costs and expenses incurred by it relating to the Registration, including
without limitation, all SEC and securities exchange, NASDAQ registration and
filing fees, and all fees and expenses of compliance by SPSS with the federal
securities laws or any applicable state blue sky laws.

     d.   RESTRICTED STOCK. The Buyer understands and agrees, as follows:

          (i)   That the Shares are not currently subject to a registration
                statement under the 1933 Act, and are issued pursuant to
                exemptions from registration under the 1933 Act which exemptions
                depend, among other things, on the bona fide nature of their
                investment intent.

          (ii)  That Buyer shall not transfer the Shares except in compliance
                with the provisions of the 1933 Act. Any proposed transferee of
                any of the Shares shall agree to take and hold such securities
                upon the conditions set forth in Section 4(d)(iii) hereof.

          (iii) Until the Registration Statement is declared effective, each
                certificate representing any of such Shares shall be stamped or
                otherwise imprinted with a legend in substantially the following
                form (in addition to any legend required under applicable state
                securities laws):

                THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED
                FOR INVESTMENT UNDER AN EXEMPTION FROM THE REGISTRATION
                REQUIREMENTS OF THE SECURITIES ACT OF 1933. SUCH SHARES MAY NOT
                BE OFFERED, SOLD OR TRANSFERRED IN THE ABSENCE OF AN EFFECTIVE
                REGISTRATION STATEMENT UNDER SAID ACT OR AN EXEMPTION THEREFROM
                OR IN CONTRAVENTION OF THE AGREEMENT COVERING THE PURCHASE OF
                THESE SHARES AND RESTRICTING THEIR TRANSFER.

                When the Shares may be sold pursuant to the Registration
                Statement, SPSS will, upon request of the Buyer, cause SPSS's
                transfer agent to exchange the share certificates legended as
                set forth above for unlegended share certificates.

          (iv)  Unless a registration statement under the 1933 Act covering
                transactions in the SPSS Common Stock to be received by the
                Buyer pursuant to this Agreement has been declared effective by
                the SEC and such registration


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                statement remains effective at the time of transfer, each holder
                of shares of SPSS Common Stock to be received by the Buyer
                pursuant to this Agreement shall comply in all respects with the
                provisions of this Section 4(d). Prior to any proposed transfer
                of any such securities, the holder thereof shall give written
                notice to SPSS of such holder's intention to effect such
                transfer and shall comply with the requirements set forth in the
                balance of this section. Each such notice shall describe the
                manner and circumstances of the proposed transfer in reasonable
                detail, and shall be accompanied by (1) a written opinion of
                legal counsel who shall be reasonably satisfactory to SPSS,
                addressed to SPSS, to the effect that the proposed transfer of
                such securities may be effected without registration under the
                1933 Act, (2) a "no action" letter from the SEC to the effect
                that the distribution of such securities without registration
                will not result in a recommendation by the staff of the SEC that
                action be taken with respect thereto, or (3) such other showing
                satisfactory to SPSS and its counsel, which satisfaction shall
                not be unreasonably withheld or delayed, that the proposed
                transfer of such securities may be effected without registration
                under the 1933 Act, whereupon the holder of such securities
                shall be entitled to transfer such securities in accordance with
                the terms of the notice delivered by the holder to SPSS.

     e.   INDEMNIFICATION. When the SPSS Common Stock held by the Buyer is
included in a registration statement under this Section 4:

          (i)   SPSS will indemnify and hold harmless the Buyer, any underwriter
                (as defined in the 1933 Act) for the Buyer and each person, if
                any, who controls the Buyer or underwriter within the meaning of
                the 1933 Act or the Securities Exchange Act of 1934, as amended
                (the "1934 Act"), against any losses, claims, damages, or
                liabilities (joint or several) to which they may become subject
                under the 1933 Act, the 1934 Act or other federal or state law,
                insofar as such losses, claims, damages, or liabilities (or
                actions in respect thereof) arise out of or are based upon any
                of the following statements, omissions or violations
                (collectively a "Violation"): (a) any untrue statement or
                alleged untrue statement of a material fact contained in such
                registration statement, including any preliminary prospectus or
                final prospectus contained therein or any amendments or
                supplements thereto, (b) the omission or alleged omission to
                state therein a material fact required to be stated therein, or
                necessary to make the statements therein not misleading, or (c)
                any violation or alleged violation by SPSS of the 1933 Act, the
                1934 Act, any state securities law or any rule or regulation
                promulgated under the 1933 Act, the 1934 Act or any state
                securities law; and SPSS will pay to the Buyer, underwriter or
                controlling person, any and all legal or other expenses
                reasonably incurred by them in connection with investigating or
                defending any such loss, claim, damage, liability, or action;
                provided, however, that the indemnity agreement contained in
                this subsection 4(e)(i) shall not apply to amounts paid in
                settlement of any such loss, claim, damage, liability, or action
                if such


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                settlement is effected without the consent of SPSS, which
                consent shall not be unreasonably withheld or delayed, nor shall
                SPSS be liable in any such case for any such loss, claim,
                damage, liability, or action to the extent that it arises out of
                or is based upon a Violation which occurs in reliance upon and
                in conformity with written information furnished by the Buyer
                any controlling person of the Buyer expressly for use in
                connection with such registration.

          (ii)  The Buyer will indemnify and hold harmless SPSS, each of its
                directors, each of its officers who has signed the registration
                statement, each person, if any, who controls SPSS within the
                meaning of the 1933 Act, any underwriter, and any controlling
                person of any such underwriter, against any losses, claims,
                damages, or liabilities (joint or several) to which any of the
                foregoing persons may become subject, under the 1933 Act, the
                1934 Act or other federal or state law, insofar as such losses,
                claims, damages, or liabilities (or actions in respect thereto)
                arise out of or are based upon any Violation, in each case to
                the extent (and only to the extent) that such Violation occurs
                in reliance upon and in conformity with written information
                furnished by the Buyer expressly for use in connection with such
                registration, and the Buyer will pay, as incurred, any legal or
                other expenses reasonably incurred by any person intended to be
                indemnified pursuant to this subsection 4(e)(ii), in connection
                with investigating or defending any such loss, claim, damage,
                liability, or action; provided, however, that the indemnity
                agreement contained in this subsection 4(e)(ii) shall not apply
                to amounts paid in settlement of any such loss, claim, damage,
                liability or action if such settlement is effected without the
                consent of the Buyer, which consent shall not be unreasonably
                withheld or delayed. In no event shall the liability of the
                Buyer hereunder be greater in amount than the dollar amount paid
                by Buyer for the Shares purchased pursuant to this Agreement.

          (iii) Promptly after receipt by an indemnified party under this
                Section 4(e) of notice of any claim, demand or the commencement
                of any action (including any governmental action), such
                indemnified party will, if a claim in respect thereof is to be
                made against any indemnifying party under this Section 4(e),
                deliver to the indemnifying party a written notice of the claim,
                demand or action and the indemnifying party shall have the right
                to participate in, and, to the extent the indemnifying party so
                desires, jointly with any other indemnifying party similarly
                noticed, to assume the defense thereof with counsel mutually
                satisfactory to the parties; provided, however, that an
                indemnified party (together with all other indemnified parties
                which may be represented without conflict by one counsel) shall
                have the right to retain one separate counsel, with the fees and
                expenses to be paid by the indemnifying party, if representation
                of such indemnified party by the counsel retained by the
                indemnifying party would be inappropriate due to a conflict of
                interests between such indemnified party and any other party
                represented by such counsel in such proceeding. The

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                failure to deliver written notice to the indemnifying party
                within a reasonable time of receipt by the indemnified party of
                notice of such claim, demand or commencement of any such action,
                if prejudicial to its ability to defend such action, shall
                relieve such indemnifying party of any liability to the
                indemnified party under this Section 4(e).

          (iv)  If the indemnification provided for in this Section 4(e) from
                the indemnifying party is unavailable to an indemnified party
                hereunder in respect of any losses, claims, damages, liabilities
                or expenses referred to therein, then the indemnifying party, in
                lieu of indemnifying such indemnified party, shall contribute to
                the amount paid or payable by such indemnified party as a result
                of such losses, claims, damages, liabilities or expenses in such
                proportion as is appropriate to reflect the relative fault of
                the indemnifying party and indemnified party in connection with
                the actions which resulted in such losses, claims, damages,
                liabilities or expenses, as well as any other relevant equitable
                considerations. The relative faults of such indemnifying party
                and indemnified party shall be determined by reference to, among
                other things, whether any action in question, including any
                untrue or alleged untrue statement of a material fact or
                omission or alleged omission to state a material fact, has been
                made by, or relates to information supplied by, such
                indemnifying party or indemnified party, and the parties'
                relative intent, knowledge, access to information and
                opportunity to correct or prevent such action. The amount paid
                or payable by a party as a result of the losses, claims,
                damages, liabilities and expenses referred to above shall be
                deemed to include any fees, charges or expenses (including fees,
                disbursements and other charges of legal counsel) reasonably
                incurred by such party in connection with any investigation or
                proceeding. No person guilty of fraudulent misrepresentation
                (within the meaning of Section 11(f) of the Securities Act)
                shall be entitled to contribution from any person.

     f.   ADDITIONAL OBLIGATIONS OF SPSS. With respect to any registration
hereunder, SPSS shall:

          (i)   Use its best efforts to cause the Registration Statement to
                become effective as soon as possible after the filing of the
                Registration Statement, but in no event later than ten (10)
                business days thereafter (assuming that the SEC does not review
                the Registration Statement). If the SEC reviews the Registration
                Statement, the Company shall use its best efforts to cause such
                Registration Statement to become effective as soon as possible
                after the filing of the Registration Statement, which efforts
                shall include, but not be limited to, promptly responding to all
                SEC comments in an appropriate manner. The Company shall use its
                best efforts to cause the Registration Statement to remain
                effective for the period set forth in Section 4.a.(i).


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          (ii)  Prepare and file with the SEC such amendments and supplements to
                the Registration Statement and the prospectus used in connection
                therewith as may be necessary to keep the Registration Statement
                effective throughout the Trading Period and to comply with the
                provisions of the 1933 Act with respect to the sale or other
                disposition of the Shares covered by the Registration Statement.

          (iii) Furnish to the Buyer such numbers of copies of the Registration
                Statement, a prospectus, including a preliminary prospectus, and
                any amendments and supplements thereto, in conformity with the
                requirements of the 1933 Act, such documents incorporated by
                reference in the Registration Statement and such other documents
                as the Buyer may reasonably request in order to facilitate the
                disposition of shares of SPSS Common Stock owned by it.

          (iv)  Promptly notify the Buyer, at any time when a prospectus
                relating thereto covered by the Registration Statement is
                required to be delivered under the 1933 Act, upon SPSS becoming
                aware that the prospectus included in the Registration
                Statement, as then in effect, includes an untrue statement of a
                material fact or omits to state a material fact required to be
                stated therein or necessary to make the statements therein not
                misleading in the light of the circumstances then existing, and
                immediately thereafter, use reasonable efforts to prepare and
                file with the SEC as soon as possible and furnish to the Buyer a
                reasonable number of copies of a supplement to or an amendment
                of such prospectus as may be necessary so that, as thereafter
                delivered to the purchasers of such Shares, such prospectus
                shall not include an untrue statement of a material fact or omit
                to state a material fact required to be stated therein or
                necessary to make the statements therein not misleading in the
                light of the circumstances under which they are made.

          (v)   Use reasonable efforts to register and qualify the securities
                covered by such registration statement under such other
                securities or Blue Sky laws of such jurisdictions as shall be
                reasonably requested by the Buyer or appropriate for the
                distribution of the securities covered by the registration
                statement.

          (vi)  To the extent required by NASDAQ requirements, notify NASDAQ of
                the issuance of the shares of SPSS Common Stock covered by such
                registration.


     g.   REPORTS UNDER THE EXCHANGE ACT. With a view to making available to the
Buyer the benefits of Rule 144 promulgated under the 1933 Act and any other rule
or regulation of the SEC that may at any time permit the Buyer to sell
securities of SPSS to the public without registration, SPSS agrees to use its
reasonable efforts to:


                                       11
<PAGE>   12

          (i)   make and keep public information available, as those terms are
                understood and defined in Rule 144, at all times;

          (ii)  file with the SEC in a timely manner all reports and other
                documents required of SPSS under the 1933 Act and the 1934 Act;
                and

          (iii) furnish to the Buyer forthwith upon request a written statement
                by SPSS that it has complied with the reporting requirements of
                Rule 144 and of the 1933 Act and the 1934 Act, a copy of the
                most recent annual or quarterly report of SPSS, and such other
                reports and documents so filed by SPSS as may be reasonably
                requested in availing the Buyer of any rule or regulation of the
                SEC permitting the selling of any securities of SPSS held by it
                without registration.


     h.   THIRD-PARTY REGISTRATION RIGHTS. Until the Registration Statement
becomes effective, (i) SPSS shall not grant future registration rights to any
third party without Buyer's prior written consent, which consent shall not be
unreasonably withheld or delayed (provided, however, that this subsection
4(h)(i) shall not apply to any registration rights of any third party granted
prior to the date hereof), and (ii) Buyer may assign its registration rights
granted hereunder to one or more of its affiliates.

     5.   ATTENDANCE AT MEETINGS OF SPSS INDUSTRY ADVISORY BOARD. For so long as
the Buyer holds at least ten percent (10%) of the Shares, Richard Gorman or
another individual designated by the Buyer, in Buyer's sole discretion, (which
designee shall be reasonably acceptable to SPSS) shall be entitled to attend (at
the Buyer's expense) all meetings of SPSS's industry advisory board (the
"Industry Advisory Board"). SPSS shall give the Buyer adequate notice of
meetings of SPSS's Industry Advisory Board, provided, however, that SPSS
reserves the right to exclude such representative from access to any material or
meeting or any portion thereof if SPSS reasonably believes upon advice of
counsel that such exclusion is necessary to preserve the attorney-client
privilege or to protect highly confidential proprietary information. The Buyer
shall be entitled to receive all written materials and other information given
to directors in connection with any meeting of the Industry Advisory Board as
soon as practicable after such materials and other information have been given
to the other attendees thereof. The Buyer shall not be entitled to attend, or
have any individual designated by the Buyer attend, any meetings of the Board of
Directors of SPSS without the express approval of an officer or the Board of
Directors of SPSS.

     6.   CONDITIONS TO CLOSING

     a.   CONDITIONS TO THE BUYER'S OBLIGATION. The obligation of the Buyer to
purchase and pay for the Shares to be purchased by it at the Closing is subject
to the following conditions (all of which, other than breaches of
representation, warranties and covenants not known to that Buyer at Closing,
shall be deemed satisfied or waived by the Buyer at or prior to the Closing in
the event all of the transactions contemplated to be effected at the Closing are
consummated and all or any of which in any case may be waived by the Buyer at or
prior to Closing):


                                       12
<PAGE>   13

          (i)   REPRESENTATIONS AND WARRANTIES. Each of the representations and
                warranties of SPSS set forth in Section 3 hereof shall be true,
                accurate and correct on and as of the Closing with the same
                effect as though such representations and warranties had been
                made as of the Closing.

          (ii)  PERFORMANCE. SPSS shall have performed and complied with all
                agreements, obligations, and conditions contained in this
                Agreement that are required to be performed or complied with by
                it on or before the Closing.

          (iii) CLOSING DOCUMENTS. SPSS shall have delivered to the Buyer each
                of the documents set forth in Section 7.a.

          (iv)  QUALIFICATIONS. All authorizations, approvals or permits, if
                any, of any governmental authority or regulatory body of the
                United States or of any state that are required in connection
                with the lawful issuance and sale of the Shares pursuant to this
                Agreement shall be duly obtained and effective as of the
                Closing.

          (v)   PROCEEDINGS AND DOCUMENTS. All corporate and other proceedings
                in connection with the transactions contemplated at the Closing
                and all documents incident thereto shall be reasonably
                satisfactory in form and substance to the Buyer's special
                counsel, and it shall have received all such counterpart
                original and certified or other copies of such documents as it
                may reasonably request.

     b.   CONDITIONS TO SPSS'S OBLIGATION. The obligation of SPSS to sell and
issue the Shares to the Buyer at Closing is subject to the following conditions
(all of which shall be deemed satisfied or waived by SPSS at or prior to Closing
in the event all of the transactions contemplated to be effected at the Closing
are consummated and all or any of which in any case may be waived by SPSS at or
prior to Closing):

          (i)   REPRESENTATIONS AND WARRANTIES. The representations and
                warranties of the Buyer set forth in Section 2 hereof shall be
                true, accurate and correct on and as of the Closing with the
                same effect as though such representations and warranties had
                been made as of the Closing.

          (ii)  SECURITIES LAW QUALIFICATION. The offer and sale to the Buyer of
                the Shares shall be qualified or exempt from qualification under
                all applicable federal and state securities laws.

          (iii) PERFORMANCE. The Buyer shall have performed and complied with
                all agreements, obligations and conditions contained in this
                Agreement that are required to be performed or complied with by
                it on or before the Closing.


                                       13
<PAGE>   14

     7.   CLOSING DELIVERIES

     a.   CLOSING DELIVERIES OF SPSS. The Buyer shall have received prior to or
at the Closing all of the following documents, each in form and substance
reasonably satisfactory to the Buyer and its counsel:

          (i)   A certificate of the Chief Executive Officer and the Chief
                Financial Officer of SPSS stating that (a) the representations
                and warranties of SPSS set forth in Section 3 hereof are true,
                accurate and correct on and as of the Closing, and (b) all
                agreements, obligations and conditions contained in this
                Agreement required to be performed and complied with by SPSS
                prior to or at the Closing have been performed as of the Closing
                and (c) that there shall have been no adverse change in the
                business, affairs, operations, properties, assets or condition
                of SPSS since June 30, 2001.

          (ii)  A stock certificate evidencing the Shares.

          (iii) Certified copies of the resolutions duly adopted by SPSS's board
                of directors authorizing the execution, delivery and performance
                of this Agreement and each of the other agreements contemplated
                hereby, the issuance and sale of the Shares and the consummation
                of all other transactions contemplated by this Agreement.

          (iv)  An opinion of Ross & Hardies, counsel for SPSS, dated as of the
                Closing, in the form attached hereto as Exhibit A.

          (v)   A certificate of good standing issued by the Secretary of State
                of the State of Delaware.

          (vi)  Copies of all third party and governmental consents, approvals
                and filings required in connection with the consummation of the
                transactions hereunder.

     b.   CLOSING DELIVERIES OF THE BUYER. SPSS shall have received prior to or
at the Closing all of the following materials or documents, each in the form and
substance reasonably satisfactory to SPSS and its counsel:

          (i)   The Purchase Price.

          (ii)  A certificate of the Chief Financial Officer of the Buyer
                stating that the representations and warranties of the Buyer set
                forth in Section 2 hereof are true, accurate and correct in all
                material respects on and as of the Closing and that all
                agreements, obligations and conditions contained in this
                Agreement required to be performed and complied with by the
                Buyer prior to or at the Closing have been performed as of the
                Closing.


                                       14
<PAGE>   15

     8.   MISCELLANEOUS

     a.   NO WAIVER; CUMULATIVE REMEDIES. No failure or delay on the part of any
party to this Agreement in exercising any right, power or remedy hereunder shall
operate as a waiver thereof; nor shall any single or partial exercise of any
such right, power or remedy preclude any other or further exercise thereof or
the exercise of any other right, power or remedy hereunder. The remedies herein
provided are cumulative and not exclusive of any remedies provided by law.

     b.   AMENDMENTS, WAIVERS AND CONSENTS. This Agreement may be amended only
by an instrument in writing signed by both parties hereto. Any waiver or consent
may be given subject to satisfaction of conditions stated therein and any waiver
or consent shall be effective only in the specific instance and for the specific
purpose for which given.

     c.   BINDING EFFECT; ASSIGNMENT. This Agreement shall be binding upon and
inure to the benefit of SPSS and the Buyer and their respective heirs,
successors and assigns.

     d.   SURVIVAL OF REPRESENTATIONS AND WARRANTIES. All representations and
warranties made in this Agreement or any other instrument or document delivered
in connection herewith, shall survive the execution and delivery hereof or
thereof and shall terminate one year from the date of this Agreement.

     e.   PRIOR AGREEMENTS. This Agreement and the Mutual Non-Disclosure
Agreement attached as Exhibit B to the Letter of Intent dated June 28, 2001
between the Buyer and SPSS, and any related documents constitute the entire
agreement between the parties hereto pertaining to the subject matter hereof,
and any and all other written or oral agreements relating to the subject matter
hereof existing between the parties hereto are expressly canceled.

     f.   SEVERABILITY. If any provision of this Agreement shall be invalid or
unenforceable in any jurisdiction, such invalidity or unenforceability shall not
affect the validity or enforceability of the remainder of this Agreement or the
validity or enforceability of this the Agreement in any other jurisdiction.

     g.   GOVERNING LAW. This Agreement shall be governed by, and construed in
accordance with the internal laws of the State of California, without giving
effect to its conflict of laws principles.

     h.   HEADINGS. Article, section and subsection headings in this Agreement
are included herein for convenience of reference only and shall not constitute a
part of this Agreement for any other purpose.

     i.   COUNTERPARTS. This Agreement may be executed in any number of
counterparts, all of which taken together shall constitute one and the same
instrument, and any of the parties hereto may execute this Agreement by signing
any such counterpart.

     j.   FURTHER ASSURANCES. From and after the date of this Agreement, upon
the request of SPSS, the Buyer shall execute and deliver such instruments,
documents and other


                                       15
<PAGE>   16

writings as may be reasonably necessary to confirm and carry out and to
effectuate fully the intent and purposes of this Agreement and the Shares.

     9.   NOTICES. Any notice required or permitted hereunder shall be given in
writing (unless otherwise specified herein) and shall be deemed effectively
given, (i) on the date delivered, (a) if by personal delivery, or (b) if advance
copy is given by fax, (ii) seven business days after deposit in the United
States Postal Service by regular or certified mail, or (iii) three business days
mailing by international express courier, with postage and fees prepaid,
addressed to each of the other parties thereunto entitled at the following
addresses, or at such other addresses as a party may designate by ten days
advance written notice to each of the other parties hereto:



          SPSS:       SPSS Inc.
                      233 South Wacker Drive
                      Chicago, Illinois 60606
                      Attention: Jack Noonan
                                 President and Chief Executive Officer
                      Facsimile: 312-651-3558

                      with a copy to:

                      Lawrence R. Samuels, Esq.
                      Ross & Hardies
                      150 North Michigan Avenue
                      Suite 2500
                      Chicago, Illinois  60601
                      Facsimile: 312-750-8600

          BUYER:      Siebel Systems, Inc.
                      2207 Bridgepointe Parkway
                      San Mateo, California 94404
                      Attention: Vice President, Legal Affairs
                      Facsimile: 650-477-7343


     10.  MOST FAVORED NATION. During the six-month period after the Closing,
SPSS shall not issue or sell any security of SPSS at less than 95% of the
then-current ten-day average trading price of the SPSS Common Stock or on terms
otherwise more favorable to those offered to Buyer without Buyer's prior written
consent, which consent shall not be unreasonably withheld or delayed. This
provision shall not apply to shares of capital stock issued upon exercise of
SPSS stock options, shares issued pursuant to SPSS's employee stock purchase
plan or shares issued in connection with a merger with or acquisition of the
stock or assets of another entity.


                                       16
<PAGE>   17

     11.  NO PUBLICITY. Except to the extent required by applicable law or a
court of competent jurisdiction, SPSS shall not make any public announcement
that refers to or identifies Buyer as an investor in SPSS without Buyer's prior
written consent which consent shall not be unreasonably withheld or delayed.


     IN WITNESS WHEREOF, this Agreement has been duly executed by the parties
hereto as of the date set forth below.


                               BUYER:


                               SIEBEL SYSTEMS, INC., a Delaware corporation


                               By:
                                  ------------------------------------------
                                    Name:
                                    Title:


                               Dated:
                                     ---------------------------------------





THIS AGREEMENT HAS BEEN ACCEPTED AS OF THE DATE SET FORTH BELOW.



SPSS:

SPSS INC., a Delaware corporation



By:
   -----------------------------------------
       Jack Noonan
       President and Chief Executive Officer


Dated:
      --------------------------------------



                                       17