Document:

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                                                                   Exhibit 10.47

April 1, 2002

Mary A. Palermo
Co-Chief Operating Officer
Aspen Technology, Inc.
Ten Canal Park
Cambridge, MA 02141

Dear Mary:

In consideration of your position, assisting with the transition of the Company
to a new organization, and future work, I propose the following terms of
employment:

COMPENSATION AND EMPLOYMENT

     1)   You will continue to be employed by AspenTech as Executive Vice
          President and Co-Chief Operating Officer at least until September 30,
          2002. During this time you will report to Larry Evans, Chairman. You
          will focus on execution of our Aspen 2002 Strategy and implementing
          the organizational changes. If we acquire Denver, this will be an
          important component of your responsibilities and activities.

     2)   You will continue at your present level of compensation through FY02.
          You will be eligible for a bonus for FY02 on the same basis as the
          other comparable members of the executive management team. You will be
          eligible for a salary increase at such time as any other members of
          the executive management team. You will continue to receive grants of
          stock options comparable to other members of the executive management
          period.

     3)   Effective October 1, 2002 you will work in business development for
          AspenTech for a period of 15 months until December 31, 2003 ("BD
          Period"). During that time you will continue to be paid at your
          present base salary. Your stock options will continue to vest during
          this period. AspenTech will continue to provide an office, secretarial
          assistance, telephone, and email account during this period. Your
          responsibilities will be primarily to be provide advice, guidance and
          business development services, but not to undertake major projects
          that would involve a significant commitment of effort.

     4)   The Company and you may, by mutual agreement, decide that you will
          remain in your present position or a new position for an extended
          period beyond September 30, 2002. If this happens, your rate of pay
          and bonus opportunity for this extended period will be determined by
          mutual agreement, but will not be reduced, and the 15-month BD Period
          will begin immediately after the last day of such extended employment
          as agreed to under this paragraph 4.

     5)   On or before the end of the BD Period, the Company and you may, by
          mutual agreement, decide that you will remain in a business
          development position beyond December 31, 2003. In such event your rate
          of pay will be determined by mutual agreement and your stock options
          would continue to vest during such extended period.

     6)   You agree to be fully supportive of the new organization and
          management and to do your best to help us achieve an enthusiastic
          transition.

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     7)   You agree to the terms and conditions of Addendum A to this letter on
          your non-compete, non-solicitation, and confidentiality agreements,
          and that such obligations will be in force and effect for the later of
          the period ending December 31, 2004, or two years after termination of
          employment.

     8)   Your compensation, benefits and employment will be structured to
          achieve as favorable tax and employment treatment as is possible and
          not otherwise materially detrimental to the interests of the Company.

This Agreement shall be governed by and construed in accordance with the laws of
the Commonwealth of Massachusetts. The Federal and State Courts in the
Commonwealth of Massachusetts shall have exclusive jurisdiction over all claims
brought in connection with this Agreement.

By signing a copy of this letter you hereby indicate your agreement to the terms
and conditions set out in this letter and Addendum A.

                                  ASPEN TECHNOLOGY, INC.

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

                                  Title:  Chairman and Chief Executive Officer
                                        ---------------------------------------

Accepted and Agreed to this ___ day of _______, 2002.

/s/ Mary A. Palermo
---------------------------
Mary A. Palermo

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                                   Addendum A
               NON-COMPETE, NON-SOLICITATION, AND CONFIDENTIALITY
               --------------------------------------------------

AGREEMENT NOT TO COMPETE. Mary A. Palermo (the "Employee") agrees that, while
serving as an Employee of the Company, she will not serve as an employee or
director of any business entity other than the Company and its affiliates that
is a competitor of the Company, but may serve as a director of a reasonable
number of not-for-profit corporations and may devote a reasonable amount of time
to charitable and community service. In consideration of the payments and
agreements hereunder, the Employee shall not solicit the Company's, or its
affiliates' or subsidiaries' (collectively, the "AspenTech Companies") customers
with whom Employee has dealt during the one year prior to the Termination Date,
either (i) to cease to do business with the AspenTech Companies, or (ii) to do
business with any other firm, partnership, or entity, in actual or proposed
competition with the AspenTech Companies. The Employee may hold stock or a
limited partnership interest of 5% or less in any publicly traded entity without
violating this Agreement.

AGREEMENT NOT TO SOLICIT. In consideration of the payments and agreements
hereunder, the Employee shall not solicit any employee of the AspenTech
Companies to leave such employment or to provide services to the Employee or any
other business entity, whether or not the Employee is employed by such entity,
or the Employee has a material financial interest therein.

CONFIDENTIAL INFORMATION: NON-DISCLOSURE. Employee acknowledges that the
business of the AspenTech Companies is highly competitive and that the Company
has provided and will provide Employee with access to Confidential Information
relating to the business of the AspenTech Companies. "Confidential Information"
means and includes the AspenTech Companies' confidential and/or proprietary
information and/or trade secrets that have been developed or used and/or will be
developed and that cannot be obtained readily by third parties from outside
sources. Confidential Information includes, by way of example and without
limitation, the following: information regarding customers, employees,
contractors, and the industry not generally known to the public; strategies,
methods, books, records, and documents; technical information concerning
products, equipment, services, and processes; procurement procedures and pricing
techniques; the names of and other information concerning customers, investors,
and business affiliates (such as contact name, service provided, pricing for
that customer, amount of services used, credit and financial data, and/or other
information relating to the AspenTech Companies' relationship with that
customer); pricing strategies; plans and strategies for expansion or
acquisitions; budgets; customer lists; electronic databases; models;
specifications; computer programs; internal business records; contracts
benefiting or obligating the AspenTech Companies; bids or proposals submitted to
any third party; technologies and methods; training methods and training
processes; organizational structure; salaries of personnel; payment amounts or
rates paid to consultants or other service providers; and other such
confidential or proprietary information. Employee acknowledges that this
Confidential Information constitutes a valuable, special, and unique asset used
by the AspenTech Companies in their business to obtain a competitive advantage
over their competitors. Employee further acknowledges that protection of such
Confidential Information against unauthorized disclosure and use is of critical
importance to the AspenTech Companies in maintaining their competitive position.
Confidential Information shall not include any information that is contained in
a printed publication or is or becomes publicly known through no wrongful act or
failure to act on the part of the Employee.

Employee agrees that Employee will not, at any time during or after Employee's
employment with Company, make any unauthorized disclosure of any Confidential
Information of the AspenTech Companies, or make any use thereof, except in the
carrying out of her employment responsibilities hereunder. Employee also agrees
to preserve and protect the confidentiality of third party Confidential
Information to the same extent, and on the same basis, as the AspenTech
Companies' Confidential Information.<PAGE>

                                                                   Exhibit 10.48

                              EMPLOYMENT AGREEMENT

     THIS EMPLOYMENT AGREEMENT dated as of May 9, 2002 (this "Agreement") is
entered into between Aspen Technology, Inc., a Delaware corporation ("Aspen")
and Wayne Sim (the "Employee").

                              PRELIMINARY STATEMENT

     A. On the date hereof, Aspen is entering into an agreement to acquire all
of the outstanding capital stock of AEA Technology Canada Ltd., and the other
corporate members of the Hyprotech Group, a Canadian Corporation, (the
"Company"), pursuant to a Sale and Purchase Agreement dated the date hereof
between Aspen and AEA Technology Plc (the "Purchase Agreement").

     B. The Employee has been employed by the Company for a number of years and
is currently employed by the Company as its Chief Executive Officer. The
Employee possesses an intimate knowledge of the business and affairs of the
Company and its policies, methods, personnel and operations.

     C. This Agreement is made by the Employee pursuant to the Purchase
Agreement, in connection with the proposed merger and the other transactions
contemplated by the Purchase Agreement.

     D. From and after the date hereof, the Employee is willing to commit
himself to serve Aspen upon the terms and conditions set forth herein.

     Now, THEREFORE, Aspen and the Employee hereby agree as follows:

1.   EMPLOYMENT

     Aspen shall employ the Employee, and the Employee hereby accepts
employment, on the terms and conditions set forth in this Agreement. The initial
title of the Employee shall be Chief Product Officer, reporting to David
McQuillin. At all times during the Initial Term (as defined in Section 6) and
any subsequent effective period of this Agreement, the Employee shall use
commercially reasonable efforts to perform his employment duties to the best of
his skill and ability. The Employee shall devote his full-time business time,
attention and energies to the business interests of Aspen.

2.   COMPENSATION

     (a) BASE SALARY. During the Term, as the Employee's regular salary for his
employment as described in Section 1, Aspen shall pay the Employee a salary (the
"Base Salary") initially at the annual rate of three hundred thirty thousand
Canadian Dollars (330,000). Such Base Salary shall be subject to review
thereafter in accordance with either Aspen's standard salary review policies,
but in no event shall the Base Salary be reduced below such initial amount. The
Base Salary shall be paid in equal installments not less frequently than monthly
and shall be prorated for any period of service less than a full year.

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     (b) BONUSES. The Employee shall be eligible for performance-related pay,
established initially as 50% of Base Salary, upon performance criteria
established by the Chief Executive Officer of Aspen, subject to established
Aspen Policy regarding funding and payment of Bonus opportunities.

     (c) OPTIONS. The Employee shall be eligible for 30,000 option grants
subject to approval of the Board of Directors.

     (d) TAXES. All salary and other compensation payable by Aspen to the
Employee shall be subject to applicable withholding taxes.

3.   EXPENSES

     Subject to such policies as may be established from time to time by the
Board of Directors, Aspen shall reimburse the Employee for all reasonable
out-of-pocket expenses incurred during the Initial Term and any subsequent
effective period of this Agreement in connection with performance of his duties
hereunder, including reasonable travel expenses. Reimbursement by Aspen as
aforesaid shall occur upon submission to Aspen by the Employee of an itemized
account of such expenses in reasonable detail.

4.   BENEFITS

     During the Term, the Employee shall be entitled to participate in or
receive benefits equivalent in Canada to those received by other executives of
Aspen under any group life, hospitalization or disability plan, health and
dental care program, 401(k) plan, pension plan, vacation policy or similar
benefit plans or arrangements made generally available by Aspen to its
employees, subject to and on a basis consistent with the terms, conditions and
overall administration of such plans and arrangements. To the extent possible
under Aspen's benefit plans and arrangements, the Employee shall receive credit
for time served at the Company as if such time had been served for Aspen.

5.   INVENTION, NON-DISCLOSURE AND NON-COMPETITION

     (a) CONFIDENTIALITY AND PROPRIETARY RIGHTS AGREEMENT. Contemporaneously
herewith, the Employee is executing and delivering to Aspen a CONFIDENTIALITY
AND PROPRIETARY RIGHTS Agreement in the form attached as EXHIBIT 1. The terms of
such agreement are hereby incorporated and made a part of this Agreement, as if
set forth herein.

     (b) NON-COMPETITION AGREEMENT. Contemporaneously herewith, the Employee is
executing and delivering to Aspen a Non-Competition Agreement in the form
attached hereto as EXHIBIT 2. The terms of such agreement are hereby
incorporated and made a part of this Agreement, as if set forth herein.

6.   TERM AND TERMINATION

                                      -2-

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     Aspen shall retain the Employee, and the Employee shall serve in the employ
of Aspen, in accordance with the terms of this Agreement for the period (the
"Initial Term") from the Completion Date of the transaction under the Purchase
Agreement and an initial period of two years or such earlier date on which this
Agreement is terminated as provided herein. This Agreement shall terminate upon
the death of the Employee and may be terminated by Aspen:

     (a)  at any time immediately upon written notice to the Employee (which
          notice shall identify the basis for termination) for "Cause," which
          shall mean (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

     (b)  upon the Employee's "disability," which shall mean the inability of
          the Employee, due to a physical or mental disability, for a period of
          90 days, whether or not consecutive, during any 365-day period to
          perform the services contemplated under this Agreement, with or
          without reasonable accommodation as that term is defined under state
          or federal law. A determination of disability shall be made by a
          physician satisfactory to both the Employee and Aspen, provided that
          if the Employee and Aspen do not agree on a physician, the Employee
          and Aspen shall each select a physician and these two together shall
          select a third physician, whose determination as to disability shall
          be binding on all parties.

In the event the Employee's employment is terminated pursuant to this Section 6,
excluding for reasons stated under this Section 6(a)(B) and (C), the Employee
shall be entitled to the greater of (i) the number of months remaining on his
non-compete obligations set forth in Exhibit 2 hereto or (ii) (a) six (6) months
prior notice of termination (after the expiration of any cure period set forth
herein) or at Aspen's option, (b) payment equal to six (6) months of the then
current fixed annual salary of the Employee, less statutory deductions, in lieu
of such notice of termination. In the event the Employee's employment is
terminated pursuant to this Section 6(a)(B) and (C), Aspen shall pay to the
Employee the compensation and benefits otherwise payable to him under Sections
2, 3 and 4 through the last day of his actual employment with Aspen.

This Agreement shall continue on after the Initial Term unless earlier
terminated under this Section 6. Aspen may terminate the employment of the
Employee at any time after the Initial Term by providing to the Employee at any
time after such period either:

     (a)  prior notice of such termination equal to six (6) months (the "Notice
          Period"); or

                                      -3-

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     (b)  a payment equal to the current fixed annual salary of the Employee,
          less statutory deductions, for that number of months equal to the
          Notice Period in lieu of such notice of termination.

7.   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, (a) 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 (b) is not intended to confer upon any
person other than the parties hereto any rights or remedies hereunder, except as
otherwise expressly provided herein. Subject to the preceding sentence, this
Agreement shall be binding upon the Employee's respective successors, heirs,
executors and administrators and will inure to the benefit of Aspen and its
successors and assigns. The obligations of the Employee are personal and shall
not be assigned by him. 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"

                                      -4-

<PAGE>

shall include any successor to the business of Aspen (whether direct or indirect
and whether by merger, consolidation, sale of assets or otherwise).

     (d) 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.

     (e) 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 Executive Officer

           To the Employee:  Wayne Sim
                             35 Spring Gate Estates SW
                             Calgary, Alberta

     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 7(e).

     (f) 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

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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.

     (g) 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.

                                      * * *

                                      -6-

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     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 and Chief Executive Officer

                              WAYNE SIM

                                         /s/ Wayne Sim
                              -----------------------------------------------

                                      -7-

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