EXHIBIT 10.57
                                                                   -------------




May 12, 2009



Mr. Roger D. Thomas
[address omitted]

Dear Roger,

RE:  TERMINATION OF EMPLOYMENT AND RETIREMENT-THIS  SUPERSEDES OUR LETTER OF
     MAY 1, 2009

This  letter  confirms  our  discussions   regarding  the  termination  of  your
employment  with  Nexen Inc.  ("Nexen").  The terms set forth  below  constitute
Nexen's offer and, by your signature,  your acceptance of this  arrangement.  On
behalf of Nexen,  I want to express my  appreciation  for your past  service and
contribution, and wish you success in your future endeavours.

1.   TERMINATION  DATE AND  RETIREMENT  DATE.  Your last day of employment  with
     Nexen  will be June 30,  2009  (the  "TERMINATION  DATE").  Your  effective
     retirement date for the purposes of the Pension Plan for Employees of Nexen
     Inc.  (the "PENSION  PLAN") and the Executive  Benefit Plan will be July 1,
     2009 (the  "RETIREMENT  DATE").  As outlined below, you will be required to
     utilize all outstanding  vacation time prior to your Termination Date. Once
     all of your vacation time has been utilized, Nexen may elect not to require
     you to attend at Nexen and  provide  services up to the  Termination  Date,
     this will not affect the payments and benefits provided pursuant to Section
     3 of this letter.

2.   RESIGNATION FROM CORPORATE  OFFICES.  Effective as of a mutually  agreeable
     date before the Retirement  Date,  you agree to, and will,  resign from all
     corporate offices you hold with Nexen and all affiliates of Nexen.

3.   PAYMENTS AND BENEFITS. You will receive the following payments and benefits
     in accordance with Nexen's existing  policies,  pursuant to your employment
     with Nexen and your participation in Nexen's benefit plans:

     (a)  REGULAR BASE SALARY.  You are entitled to payment of your regular base
          salary through the Termination Date.

     (b)  VACATION BENEFITS.  You will use all outstanding vacation prior to the
          Termination Date and no further payment will be due at that time.

     (c)  RETIREMENT PENSION BENEFITS. Upon your termination of employment as of
          the  Termination  Date,  you will be entitled  to receive  benefits in
          accordance with the terms of the Pension Plan,  Defined Benefit Option
          as  well as the  Executive  Benefit  Plan.  Details  will be  provided
          shortly in a separate package.

     (d)  PRE-RETIREMENT  HEALTH  AND  WELFARE  BENEFITS.  You are  entitled  to
          continue your health and welfare  benefits until the Termination  Date
          to the  extent  permitted  and in  accordance  with  the  terms of the
          applicable Nexen plan.

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Mr. Roger D. Thomas
May 12, 2009
Page 2


     (e)  POST-RETIREMENT HEALTH AND WELFARE BENEFITS. As of the date you are no
          longer  entitled  to active  employee  coverage  under the Nexen  Inc.
          benefits  program  (i.e.,  as of the  Termination  Date)  you  will be
          entitled to a retiree  benefit  consisting  of $5,000 life  insurance.
          Nexen  has   sourced  a  retiree   benefits   plan,   which   provides
          Canadian-based  retiring  employees  the option to  purchase  extended
          benefits at pooled rates directly  through  Manulife.  Please refer to
          the enclosed memo and brochure for detailed information.

     (f)  LONG-TERM  INCENTIVES.  Based on your  participation  in Nexen's Stock
          Option Plan ("the Plan"),  which  provides for  continued  vesting and
          opportunity  to exercise  options for a period of 18 months  following
          termination  for reason of  retirement,  your options will continue to
          vest in  accordance  with the Plan for a period of 18 months after the
          Termination Date. All outstanding options,  vested and unvested,  will
          expire on December 30, 2010 per the terms and  conditions of the Plan.
          A table  illustrating your current option holdings with vesting status
          is  attached  for  your  reference.  You  may  contact  Nexen's  Stock
          Administrator  at (403) 298-5295  regarding any options  transactions.
          You are solely  responsible  for  exercising  all vested stock options
          prior to the expiry of such options on December 30, 2010.

     The amounts  paid in  accordance  with this  paragraph  are gross  amounts,
     subject to  applicable  deductions  and  withholdings.  Any  amounts  under
     subparagraph  (a) of this paragraph not paid to you before the  Termination
     Date  will be paid to you in one (1)  lump sum on the  next  available  pay
     period from the Termination Date.

4.   SPECIAL SEPARATION  BENEFITS.  Contingent upon your acceptance of the terms
     of this  Agreement,  Nexen offers you,  the  following  Special  Separation
     Benefits:

     (a)  BASE SALARY. Payment of $1,100,000, which is 24 months of your regular
          base salary.

     (b)  TARGET BONUS.  Payment of $660,000,  which is 60% of your regular base
          salary and your target bonus for 24 months after the Termination Date.

     (c)  BENEFITS  UPLIFT.  Payment of  $276,600,  which  represents a benefits
          uplift of approximately 25% for 24 months.

     (d)  VEHICLE  ALLOWANCE.  Payment  of  $38,400,  which is 24 months of your
          vehicle allowance.

     (e)  EXECUTIVE  OUTPLACEMENT  SERVICES.  If you elect to receive  executive
          outplacement  services,  payment of up to $25,000 to the company  with
          which Nexen  currently  contracts in Calgary,  Alberta to provide such
          services  to  its  employees  (the   "Outplacement   Benefits").   The
          Outplacement  Benefits  must be  accessed by you within 90 days of the
          Termination Date or they are forfeited.

     The amounts paid in accordance with subparagraphs (a)-(d) of this paragraph
     are gross amounts,  subject to applicable deductions and withholdings.  The
     amounts paid in accordance  with  subparagraphs  (a)-(d) of this  paragraph
     will be paid to you on the next  available pay period from the  Termination
     Date.

5.   RETURN OF PROPERTY.  Whether or not you accept the terms of this Agreement,
     you must  return  to Nexen  any and all  items of its  property,  including
     without  limitation keys,  badge/access  card,  computers,  software,  cell
     phones,  calculators,  equipment,  credit  cards,  forms,  files,  manuals,
     correspondence,  business  records,  personnel  data,  lists of  employees,
     salary  and  benefits  information,  customer  lists  and  files,  lists of
     suppliers  and  vendors,  price  lists,  contracts,  contract  information,
     marketing plans, brochures,  catalogs, training materials, product samples,
     computer tapes, CDs, and diskettes or other

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Mr. Roger D. Thomas
May 12, 2009
Page 3


     portable media,  computer-readable  files and data stored on any hard drive
     or other installed  device,  and data processing  reports,  and any and all
     other  documents or property in your  possession or under your control.  If
     you have any  property of Nexen that is not  immediately  available to you,
     please make  arrangements  for its prompt return.  By your signature below,
     you represent that you have complied with these requirements.

6.   CONFIDENTIALITY.  You agree that the fact and terms of this Agreement shall
     be and remain confidential,  and shall not be disclosed by you to any party
     other than your spouse,  lawyer, and accountant or tax return preparer, and
     except  as  otherwise  may be  required  by law,  regulation,  or  judicial
     process.  The  fact  and  terms  of  this  Agreement  shall  be and  remain
     confidential,  and shall not be disclosed by Nexen to any party,  except as
     otherwise  may  be  required  by  law,  regulation,  or  judicial  process;
     provided,  however, that that Nexen may disclose the fact and terms of this
     Agreement   to   those  of  its   directors,   officers,   employees,   and
     representatives  who  need to know  such  information  for the  purpose  of
     administering this Agreement.

7.   INDEMNITY. The Company does agree to indemnify Roger D. Thomas from any and
     all third party actions, causes of actions, claims and demands for damages,
     loss, or injury,  suits,  debts,  sums of money,  dues,  bonds,  indemnity,
     expenses,  interest,  costs arising out of, in connection with, or relating
     to Roger D.  Thomas  having  been an  employee,  officer or director of the
     Corporation but which indemnity shall exclude any claim based on the fraud,
     gross negligence, criminal conduct or deceitful conduct of Roger D. Thomas.

8.   GOVERNING LAW AND INTERPRETATION.  This Agreement and the rights and duties
     of the parties  under it shall be governed by and  construed in  accordance
     with the laws of the Province of Alberta,  without regard for any conflicts
     of  laws  principles.  If any  provision  of this  Agreement  is held to be
     unenforceable,  such provision shall be considered separate,  distinct, and
     severable from the other remaining provisions of this Agreement,  and shall
     not  affect  the  validity  or   enforceability  of  such  other  remaining
     provisions;  and in all other respects, this Agreement shall remain in full
     force  and  effect.  If any  provision  of  this  Agreement  is  held to be
     unenforceable  as written but may be made to be  enforceable by limitation,
     then such provision shall be enforceable to the maximum extent permitted by
     applicable  law. The language of all parts of this  Agreement  shall in all
     cases be  construed  as a whole,  according  to its fair  meaning,  and not
     strictly for or against any of the parties.

9.   EXPIRATION  OF  OFFER.  Nexen's  offer of the  Special  Separation  Benefit
     described  in Paragraph 4 above will expire at 5:00 p.m. on May 20, 2009, a
     period of 8 calendar  days after you were  provided  with the terms of this
     Agreement  for your  consideration.  You may accept  this offer at any time
     before  expiration by signing this letter in the space provided below,  and
     returning  it to me.  Whether or not you execute this  Agreement,  you will
     receive the items set forth in  Paragraph 3, and are required to follow the
     obligations set forth in Paragraph 5.

10.  CONSULTATION WITH A LAWYER.  You have the right, and are encouraged by this
     paragraph, to consult with a lawyer before executing this Agreement.  Nexen
     will reimburse you for up to $300 in legal fees.

11.  VOLUNTARY AGREEMENT.  You acknowledge that your execution of this Agreement
     is  knowing  and  voluntary,  and that you  have had a  reasonable  time to
     deliberate regarding its terms.

If you agree  with the above  provisions,  please  execute  both  copies of this
letter in the space provided below as well as the attached form of Release.  You
should return one executed original to me, and maintain the

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Mr. Roger D. Thomas
May 12, 2009
Page 4


other  executed  original in your files.  The payment of the Special  Separation
Benefits  are  conditional  upon your  execution  of this  letter,  the attached
Release as well as all appropriate documentation regarding your resignation from
corporate offices as outlined in Section 2 of this letter.

Sincerely,

NEXEN INC.


By: /s/ Randy Jahrig
    -------------------------------------------
    Randy Jahrig
    Vice President, Human Resources and Corporate Services

Enclosures


ACCEPTED AND AGREED TO:


/s/ Roger D. Thomas
------------------------------------------
Roger D. Thomas


Date Signed: May 19, 2009
             -----------------------------