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Exhibit 10.59    
    

[AspenTechnology Letterhead/Logo]  

August 18,
2003 

David
L. McQuillin

President and Chief Executive Officer 

Dear
David: 

This
letter amendment references the letter agreement between you and AspenTech dated June 24, 2003 (the "Agreement") regarding your FY04 Executive Compensation Plan. Under the terms of the
Agreement, AspenTech agreed that it would grant you an option to purchase the number of shares of AspenTech common stock specified in the Agreement, contingent upon stockholder approval of the Advent
transaction (the "Option"). As you know, the Advent transaction was approved by AspenTech stockholders and closed on August 14, 2003. 

AspenTech
acknowledges that you have voluntarily agreed to reduce the number of shares subject to the Option to which you were entitled in order to make more options available for the general employee
option pool. You hereby confirm, by execution of this letter amendment, that the option granted to you on August 18, 2003 for 1,516,609 shares of AspenTech common stock constitutes full
satisfaction of AspenTech's obligations under the Agreement to grant the Option and that the terms of the Agreement do not entitle you to any additional stock option grants. All other terms of the
Agreement, including those contingent upon the closing of the Advent transaction, remain in full force and effect. 

	Best regards,	 	 	 	 
	

/s/ HELEN MOYE	
 	

/s/  DAVID L. MCQUILLIN      	
 	

Sept. 26, 2003
	
	 	
	 	

	Helen Moye	 	David L. McQuillin	 	Date
	Sr. VP Human Resources

Aspen Technology, Inc.	 	President and Chief Executive Officer	 	 

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Exhibit 10.60    
    

[AspenTechnology Letterhead/Logo]  

August 18,
2003 

Wayne
Sim

Senior Vice President, Worldwide Sales 

Dear
Wayne: 

This
letter amendment references the letter agreement between you and AspenTech dated June 24, 2003 (the "Agreement") regarding your FY04 Executive Compensation Plan. Under the terms of the
Agreement, AspenTech agreed that it would grant you an option to purchase the number of shares of AspenTech common stock specified in the Agreement, contingent upon stockholder approval of the Advent
transaction (the "Option"). As you know, the Advent transaction was approved by AspenTech stockholders and closed on August 14, 2003. 

AspenTech
acknowledges that you have voluntarily agreed to reduce the number of shares subject to the Option to which you were entitled in order to make more options available for the general employee
option pool. You hereby confirm, by execution of this letter amendment, that the option granted to you on August 18, 2003 for 421,000 shares of AspenTech common stock constitutes full
satisfaction of AspenTech's obligations under the Agreement to grant the Option and that the terms of the Agreement do not entitle you to any additional stock option grants. All other terms of the
Agreement, including those contingent upon the closing of the Advent transaction, remain in full force and effect. 

	Best regards,	 	 	 	 
	

/s/  HELEN MOYE      	
 	

/s/  WAYNE D. SIM      	
 	

Sept. 26, 2003
	
	 	
	 	

	Helen Moye	 	Wayne D. Sim	 	Date
	Sr. VP Human Resources

Aspen Technology, Inc.	 	Senior Vice President, Worldwide Sales	 	 

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Exhibit 10.61    
    

[AspenTechnology Letterhead/Logo]  

August 18,
2003 

Stephen
J. Doyle

General Counsel 

Dear
Steve: 

This
letter amendment references the letter agreement between you and AspenTech dated June 24, 2003 (the "Agreement") regarding your FY04 Executive Compensation Plan. Under the terms of the
Agreement, AspenTech agreed that it would grant you an option to purchase the number of shares of AspenTech common stock specified in the Agreement, contingent upon stockholder approval of the Advent
transaction (the "Option"). As you know, the Advent transaction was approved by AspenTech stockholders and closed on August 14, 2003. 

AspenTech
acknowledges that you have voluntarily agreed to reduce the number of shares subject to the Option to which you were entitled in order to make more options available for the general employee
option pool. You hereby confirm, by execution of this letter amendment, that the option granted to you on August 18, 2003 for 255,053 shares of AspenTech common stock constitutes full
satisfaction of AspenTech's obligations under the Agreement to grant the Option and that the terms of the Agreement do not entitle you to any additional stock option grants. All other terms of the
Agreement, including those contingent upon the closing of the Advent transaction, remain in full force and effect. 

	Best regards,	 	 	 	 
	

/s/  HELEN MOYE      	
 	

/s/  STEPHEN J. DOYLE      	
 	

Sept. 26, 2003
	
	 	
	 	

	Helen Moye	 	Stephen J. Doyle	 	Date
	Sr. VP Human Resources

Aspen Technology, Inc.	 	General Counsel	 	 

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Exhibit 10.62    
    

[AspenTechnology Letterhead/Logo]  

August 18,
2003 

C.
Steven Pringle

Senior Vice President, M/SC Business Unit 

Dear
Steve: 

This
letter amendment references the letter agreement between you and AspenTech dated June 24, 2003 (the "Agreement") regarding your FY04 Executive Compensation Plan. Under the terms of the
Agreement, AspenTech agreed that it would grant you an option to purchase the number of shares of AspenTech common stock specified in the Agreement, contingent upon stockholder approval of the Advent
transaction (the "Option"). As you know, the Advent transaction was approved by AspenTech stockholders and closed on August 14, 2003. 

AspenTech
acknowledges that you have voluntarily agreed to reduce the number of shares subject to the Option to which you were entitled in order to make more options available for the general employee
option pool. You hereby confirm, by execution of this letter amendment, that the option granted to you on August 18, 2003 for 245,008 shares of AspenTech common stock constitutes full
satisfaction of AspenTech's obligations under the Agreement to grant the Option and that the terms of the Agreement do not entitle you to any additional stock option grants. All other terms of the
Agreement, including those contingent upon the closing of the Advent transaction, remain in full force and effect. 

	Best regards,	 	 	 	 
	

/s/  HELEN MOYE      	
 	

/s/  C. STEVEN PRINGLE      	
 	

Sept. 26, 2003
	
	 	
	 	

	Helen Moye	 	C. Steven Pringle	 	Date
	Sr. VP Human Resources

Aspen Technology, Inc.	 	Senior Vice President, M/SC Business Unit	 	 

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Exhibit 10.63    
    

[AspenTechnology Letterhead/Logo]  

August 18,
2003 

Charles
Kane

Senior Vice President and CFO 

Dear
Chuck: 

This
letter amendment references the offer letter between you and AspenTech dated June 16, 2003 (the "Agreement") regarding your employment with AspenTech. Under the terms of the Agreement,
AspenTech agreed that, following stockholder approval of the Advent transaction, it would grant you an option to purchase a number of shares of AspenTech common stock which would maintain your
pre-transaction equity participation percentage in AspenTech (the "Option"). As you know, the Advent transaction was approved by AspenTech stockholders and closed on August 14,
2003. 

AspenTech
acknowledges that you have voluntarily agreed to reduce the number of shares subject to the Option to which you were entitled in order to make more options available for the general employee
option pool. You hereby confirm, by execution of this letter amendment, that the option granted to you on August 18, 2003 for 189,216 shares of AspenTech common stock constitutes full
satisfaction of AspenTech's obligations under the Agreement to grant the Option and that the terms of the Agreement do not entitle you to any additional stock option grants. All other terms of the
Agreement, including those contingent upon the closing of the Advent transaction, remain in full force and effect. 

	Best regards,	 	 	 	 
	

/s/  HELEN MOYE      	
 	

/s/  CHARLES KANE      	
 	

Sept. 26, 2003
	
	 	
	 	

	Helen Moye	 	Charles Kane	 	Date
	Sr. VP Human Resources

Aspen Technology, Inc.	 	Senior Vice President and CFO	 	 

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Exhibit 10.64    
    

[AspenTechnology Letterhead/Logo]  

August 18,
2003 

Manolis
E. Kotzabasakis

Senior Vice President, Engineering Business Unit 

Dear
Manolis: 

This
letter amendment references the letter agreement between you and AspenTech dated June 24, 2003 (the "Agreement") regarding your FY04 Executive Compensation Plan. Under the terms of the
Agreement, AspenTech agreed that it would grant you an option to purchase the number of shares of AspenTech common stock specified in the Agreement, contingent upon stockholder approval of the Advent
transaction (the "Option"). As you know, the Advent transaction was approved by AspenTech stockholders and closed on August 14, 2003. 

AspenTech
acknowledges that you have voluntarily agreed to reduce the number of shares subject to the Option to which you were entitled in order to make more options available for the general employee
option pool. You hereby confirm, by execution of this letter amendment, that the option granted to you on August 18, 2003 for 298,488 shares of AspenTech common stock constitutes full
satisfaction of AspenTech's obligations under the Agreement to grant the Option and that the terms of the Agreement do not entitle you to any additional stock option grants. All other terms of the
Agreement, including those contingent upon the closing of the Advent transaction, remain in full force and effect. 

	Best regards,	 	 	 	 
	

/s/  HELEN MOYE      	
 	

/s/  MANOLIS KOTZABASAKIS      	
 	

Sept. 26, 2003
	
	 	
	 	

	Helen Moye	 	Manolis E. Kotzabasakis	 	Date
	Sr. VP Human Resources

Aspen Technology, Inc.	 	Senior Vice President, Engineering Business Unit	 	 

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Exhibit 10.64

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