Exhibit 10.6

    Aspen Technology, Inc. Ten Canal Park   [phone] 617 949 1000   [world wide
web] www.aspentech.com     Cambridge MA 02141-2201 USA   [fax] 617 949 1030  
[e-mail] info@aspentech.com

[ASPENTECH LOGO]

June 24, 2003

Mr. Steve Pringle
Senior VP Manufacturing/Supply Chain Product Business Unit (PBU)

Dear Steve:

        I am pleased to confirm that the Compensation Committee of the AspenTech
Board of Directors has approved the following FY04 Executive Compensation Plan
for you. This Plan is contingent upon shareholder approval of the Advent
financing transaction, which is currently scheduled for August 2003.

        Your total target compensation for FY04 will be $334,000, which is
comprised of a base salary of $230,000 and a bonus target of 45%. The actual
bonus you earn will be determined by your achievement of FY04 goals. I will
communicate the details of the FY04 bonus program to you in early Q1 once the
program has been finalized and approved by the Compensation Committee.

        In addition, you will be granted options to purchase 272,200 shares of
AspenTech common stock at the Fair Market Value on the day the Advent
transaction is approved by shareholders. This grant, together with your existing
option holdings, would bring your total equity participation level to
approximately 0.400%, based on options with grant prices of $10/share or lower
on a pre-reverse split basis. In consideration for this substantial new grant,
the following conditions apply, contingent upon closing of the Advent
transaction and issuance of the options:

•For your existing stock options with pre-split grant prices of $10/share or
lower, you agree to only exercise these options in accordance with their normal
vesting schedule. In the event of your involuntary termination, or a change of
control event as redefined in the 2001/2003 stock option plan and described in
the proxy statement for the Advent transaction, this restriction will be lifted.

•Your existing employment/Change of Control agreement will be cancelled, and you
will thereafter be entitled to receive, in the event your employment is
terminated other than for cause prior to June 24, 2006, severance in an amount
equal to your annual base salary then in effect, payable over 12 months in
accordance with AspenTech's semi-monthly payroll schedule.

        Steve, I look forward to our continued work together as we drive
shareholder value.

Best regards,

/s/ David L. McQuillin

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David L. McQuillin
President and CEO
Aspen Technology, Inc.   /s/ Steve Pringle

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Steve Pringle
Senior VP Manufacturing/Supply Chain PBU
Aspen Technology, Inc.   June 24, 2003

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