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                                                                    Exhibit 10.9

                              EMPLOYMENT AGREEMENT

         THIS EMPLOYMENT AGREEMENT dated as of November 26, 2002 (this
"Agreement") is entered into between Aspen Technology, Inc., a Delaware
corporation ("Aspen") and David L. McQuillin (the "Employee").

1.       BASIS FOR AGREEMENT

         This agreement replaces the letter of September 30, 2002, and further
supplements the existing terms of employment between Aspen and the Employee,
including the Change in Control Agreement dated August 12, 1997 ("Change in
Control Agreement"), which remains in full force and effect. Aspen is continuing
to employ the Employee as a key employee of Aspen and has determined that
Employee's services are essential to the successful operation and future of
Aspen. Employee currently holds the position of President and Chief Executive
Officer. Aspen has determined that it is in its best interests to secure certain
employment commitments from Employee in consideration of providing certain
severance and compensation commitments to Employee.

2.       COMPENSATION

         Employee's compensation will be as agreed to by the Compensation
Committee of the Board of Directors.

3.       TERMINATION: NOTICE AND SEVERANCE

         (a) Upon termination of employment for any reason other than death,
             resignation without Good Reason, or for Cause, Aspen shall, in
             addition to any benefits due under written plans, pay you your base
             salary for 18 months after termination of employment.

         (b) "For Cause," means (A) a good faith finding by Aspen that the
             Employee has failed to perform his reasonably assigned duties for
             Aspen and has failed to remedy such failure within 30 days
             following written notice from Aspen to the Employee notifying him
             of such failure, (B) a good faith finding by the Board of Directors
             of Aspen that the Employee has engaged in dishonesty, gross
             negligence or misconduct, or (C) the conviction of the Employee of,
             or the entry of a pleading of guilty or NOLO CONTENDERE by the
             Employee to, any felony; or

         (c) "Good Reason" means termination by the Employee of the Employee's
             employment upon the occurrence (without the Employee's express
             written consent) of any one of the following acts or failures to
             act by Aspen unless, in the case of any act or failure to act
             described in paragraph (i), (v), or (vi) below, such act or failure
             to act is corrected prior to the date of termination specified in
             the notice of termination given in respect thereof or, in the case
             of paragraph (iii) below, such act is not objected to in writing by
             the Employee within four months after notification by Aspen to
             Employee of Aspen's intention to take the action contemplated by
             such paragraph (iii):

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             (i)   the assignment to the Employee of any duties inconsistent
                   with the Employee's status as a senior Employee officer of
                   Aspen or a meaningful alteration, adverse to the Employee, in
                   the nature or status of the Employee's responsibilities
                   (other than reporting responsibilities) from those in effect;

             (ii)  a reduction by Aspen in the Employee's annual base salary as
                   in effect on the date hereof or as the same may be increased
                   from time to time except for across-the-board salary
                   reductions similarly affecting all senior Employees of Aspen
                   and all senior Employees of any Person in control of Aspen;

             (iii) Aspen's requiring Employee to be based anywhere other than
                   the Boston Metropolitan Area except for required travel on
                   Aspen business to an extent substantially consistent with
                   Employee's present business travel obligations;

             (iv)  the failure by Aspen, without the Employee's consent, to pay
                   to the Employee any portion of the Employee's current
                   compensation, or to pay to the Employee any portion of an
                   installment of deferred compensation under any deferred
                   compensation program of Aspen, within fourteen days of the
                   date such compensation is due;

             (v)   the failure by Aspen to continue in effect any compensation
                   plan in which the Employee participates which is material to
                   the Employee's total compensation, or the failure by Aspen to
                   continue the Employee's participation therein on a basis not
                   materially less favorable, both in terms of the amount of
                   benefits provided and the level of the Employee's
                   participation relative to other participants;

             (vi)  the failure by Aspen to continue to provide Employee with
                   benefits substantially similar to those enjoyed by Employee
                   under any of Aspen' s pension, life insurance, medical,
                   health and accident, or disability plans in which Employee is
                   at any time participating, the taking of any action by Aspen
                   which would directly or indirectly materially reduce any of
                   such benefits or deprive Employee of any material fringe
                   benefit enjoyed by Employee, or the failure by Aspen to
                   provide Employee with the number of paid vacation days to
                   which the Employee is entitled on the basis of years of
                   service with Aspen in accordance with Aspen's normal vacation
                   policy.

         4. APPLICATION OF CHANGE IN CONTROL AGREEMENT

         Notwithstanding anything to the contrary herein, this Agreement shall
not apply in the event that Employee's Change in Control Agreement is deemed to
be valid, enforceable, and

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applicable, and further that Employee receives the compensation provided for
thereunder equal to or in excess of the amount provided for under this
Agreement.

5.       MISCELLANEOUS

         (a) AMENDMENTS AND WAIVERS. No amendment of any provision of this
Agreement shall be valid unless the same shall be in writing and signed by both
of the parties hereto. No waiver of any right or remedy hereunder shall be valid
unless the same shall be in writing and signed by the party giving such waiver.
No waiver by either party hereto with respect to any condition or breach
hereunder shall be deemed to extend to any prior or subsequent condition or
breach hereunder or affect in any way any rights arising by virtue of any prior
or subsequent condition or breach. No failure on the part of any party hereto to
exercise, and no delay in exercising any right hereunder shall operate as a
waiver thereof; nor shall any single or partial exercise of any such right
preclude any other or further exercise thereof or the exercise of any other
right.

         (b) CONSTRUCTION.

             (i)   The section headings contained in this Agreement are inserted
                   for convenience only and shall not affect in any way the
                   meaning or interpretation of this Agreement.

             (ii)  The language used in this Agreement shall be deemed to be the
                   language chosen by the parties hereto to express their mutual
                   intent, and no rule of strict construction shall be applied
                   against a party hereto.

             (iii) The term "including" as used herein shall not be construed so
                   as to exclude any other thing not referred to or described.

             (iv)  References herein to "Sections" shall be deemed to be to
                   sections of this Agreement, unless otherwise specified.

         (c) ENTIRE AGREEMENT; SUCCESSORS. This Agreement, including the
exhibits hereto, (i) constitutes the entire agreement, and supersedes all other
prior agreements and understandings, both written and oral, between the parties
with respect to the subject matter hereof and (ii) is not intended to confer
upon any person other than the parties hereto any rights or remedies hereunder,
except as otherwise expressly provided herein. For purposes of clarification,
this Agreement does not replace or otherwise amend your Change in Control
Agreement dated August 12, 1997, which remains in full force and effect. In the
event of a termination that qualifies you for compensation under both
agreements, then the terms of the Change in Control Agreement shall control.

         (d) The obligations of Aspen may be assigned by Aspen, provided that
such obligations shall be assumed by such subsidiary without modification. For
all purposes of this Agreement, the term "Aspen" shall include any successor to
the business of Aspen (whether direct or indirect and whether by merger,
consolidation, sale of assets or otherwise).

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         (e) GOVERNING LAW. This Agreement shall be governed by and construed in
accordance with the internal laws of the Commonwealth of Massachusetts without
giving effect to any choice or conflict of law provision or rule (whether of the
Commonwealth of Massachusetts) or any other jurisdiction) that would cause the
application of laws of any jurisdictions other than those of the Commonwealth of
Massachusetts.

         (f) NOTICES. All notices, instructions, demands, claims, requests and
other communications given hereunder or in connection herewith shall be in
writing. Any such communication shall be sent either (a) by registered or
certified mail, return receipt requested, postage prepaid, or (b) via a
reputable nationwide overnight courier service, in each case to the address set
forth below. Any such communication shall be deemed to have been delivered two
business days after it is sent by registered or certified mail, return receipt
requested, postage prepaid, or one business day after it is sent via a reputable
nationwide overnight courier service.

                  To Aspen:        Aspen Technology, Inc.
                                   Ten Canal Park
                                   Cambridge, Massachusetts 02141
                                   Facsimile: 617.577.0722
                                   Attention:  Chief Employee Officer

                  To the Employee: Mr. David L. McQuillin
                                   [home address]

         Either party hereto may give any notice, instruction, demand, claim,
request or other communication hereunder using any other means (including
personal delivery, expedited courier, messenger service, telecopy, telex,
ordinary mail or electronic mail), but no such communication shall be deemed to
have been duly given unless and until it actually is received by the party for
which it is intended. Either party hereto may change the address to which
notices, instructions, demands, claims, requests and other communications
hereunder are to be delivered by giving the other party hereto notice in the
manner set forth in this Section.

         (g) SEVERABILITY. Any term or provision of this Agreement that is
invalid or unenforceable in any situation in any jurisdiction shall not affect
the validity or enforceability of the remaining terms and provisions hereof or
the validity or enforceability of the offending term or provision in any other
situation or in any other jurisdiction. If the final judgment of a court of
competent jurisdiction declares that any term or provision hereof is invalid or
unenforceable, the parties hereto agree that the court making the determination
of invalidity or unenforceability shall have the power to limit the term or
provision, to delete specific words or phrases, or to replace any invalid or
unenforceable term or provision with a term or provision that is valid and
enforceable and that comes closest to expressing the intention of the invalid or
unenforceable term or provision, and this Agreement shall be enforceable as so
modified.

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         (h) SIGNATURES. This Agreement may be executed in counterparts, each of
which shall be deemed an original but both of which together shall constitute
one and the same instrument. This Agreement may be executed by facsimile
signature.

                               * * *

         IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first set forth above.

                                       ASPEN TECHNOLOGY, INC.

                                       By: /s/ Lawrence B. Evans
                                           ------------------------------------
                                           Name: Lawrence B. Evans
                                           Title: Chairman

                                       /s/ David McQuillin
                                           ------------------------------------
                                           David McQuillin






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