Exhibit 10.21



                                 UnitedGlobalCom


July 10, 2000

John Porter
2A Hillside Avenue
Vaucluse, NSW 2030
AUSTRALIA

Re:  Employment Terms

Dear John:

     This letter sets forth the agreement  ("Agreement)  among  UnitedGlobalCom,
Inc.  ("UGC),  Austar  United  Communications  Limited  ("Company)  and yourself
concerning  your continued  employment with UGC and secondment to the Company in
Australia.  UGC  may  reassign  you to a  different  affiliated  company  and/or
location during the term of this  Agreement.  The terms of the Agreement are set
forth below.

     This Agreement  supersedes and replaces the  employment  agreement  between
UnitedGlobalCom,  Inc.,  CTV Pty  Limited  and STV Pty  Limited,  and you  dated
February 18, 1995, as amended on November 27, 1995, May 16, 1995, March 9, 1995,
May 31, 1996, and June 5, 1996 ("1995  Agreement") and any and all other written
or oral  agreements  between  you,  UGC and/or an  affiliate of UGC and all such
previous  agreements  are  hereby  rendered  null  and  void.  The  terms of the
Agreement are set forth below.


1.  Effective Date: June 1, 2000

2.  Title and Job   Chief  Executive  Officer of the  Company
    Description:    You  will  report  to the  Board of the  Company  and to the
                    President and COO of UGC.

3.  Term:           The  term  of  your  employment  ("Term")  commences  on the
                    Effective  Date and  ends on May 30,  2003,  subject  to the
                    other terms of this Agreement.

4.  Wages:          You will be paid on a bi-weekly basis, at a rate equal to an
                    annual  salary of US $277,750,  commencing  on the Effective
                    Date. This wage,  together with the other benefits described
                    below, represents your total compensation package.

5.  Bonus:          You will be eligible  for an annual bonus of up to a maximum
                    amount of fifteen  percent  (15%) of your base salary.  Your
                    eligibility  for  the  bonus  will  be  based  on  both  the
                    performance of the Company and your individual  performance.
                    The granting of the bonus is in the sole  discretion  of the
                    Board of the Company.

<PAGE>
                                                      Extension Letter Agreement
                                                                     John Porter
                                                                    July 7, 2000

6.  Cost of Living  You will be paid a cost of living differential,  for housing
    Differential:   and goods and services,  in accordance  with the policies of
                    UGC and as may be  recommended  by a third party  consultant
                    used by UGC. Such payment will be made on the normal payroll
                    dates.

7.  Automobile:     The Company will pay for an  automobile  and all  automobile
                    operating costs, to include gas,  insurance and maintenance,
                    in accordance with UGC policy.

8.  Benefits:       You and your  family will  continue  to be eligible  for the
                    standard  benefit package offered by UGC, in accordance with
                    the  policy  guidelines  set forth by UGC and its  insurance
                    carriers. You will continue to be eligible to participate in
                    UGC's 401(k) plan in accordance with the plan guidelines.

9.  Tuition:        You  will be  reimbursed  for the cost of  tuition  fees and
                    transportation   for  your   children   enrolled  in  grades
                    kindergarten  through 12 (or the equivalent) who reside with
                    you in Australia as approved in advance by your supervisor.

10. Stock Options:  On July 20, 1999, you were issued 4,880,850 stock options at
                    an  exercise  price of  AUD$1.80,  pursuant to the terms and
                    conditions  of the  Company's  Executive  Share  Option Plan
                    ("the  Plan").  You will be eligible  for  additional  stock
                    option  grants in the future.  The granting of stock options
                    is in the sole discretion of The Board of the Company.

11. Tax             Your taxes will be  equalized  in  accordance  with the "Tax
    Equalization:   Equalization Policy" of United. In general terms, this means
                    that the Company will bear the overall  worldwide tax burden
                    to the extent it exceeds  your  hypothetical  tax  liability
                    (within some limitations) had you remained in the U.S.

                    If it is  determined  by  United  and  its  independent  tax
                    consultants that under United's Tax Equalization  Policy you
                    owe taxes as a result of your assignment, you agree that you
                    will pay such  amount  to  United.  If it is  determined  by
                    United  and  its  independent  tax  consultants  that  under
                    United's Tax Equalization Policy, United owes you taxes as a
                    result of your  assignment in the foreign  location,  United
                    agrees  to pay you  such  amount.  In the  event  you do not
                    submit  information  necessary to complete  your tax returns
                    for a given tax year by the date  required by  United's  tax
                    consultant  for  timely  filing or in the event you have not
                    paid  amounts  owing to United  under  the Tax  Equalization
                    Policy  for  prior  years,  you will have no right to be tax
                    equalized  for that tax year for which a tax return is to be
                    prepared and, in United's sole discretion,  United may elect
                    not to tax equalize you for such year.

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<PAGE>
                                                      Extension Letter Agreement
                                                                     John Porter
                                                                    July 7, 2000


12. Vacation:       You will  continue  to receive  twenty (20) days of vacation
                    per  anniversary  year,  which  accrues on a monthly  basis,
                    taken in accordance  with UGC policy.  Your original date of
                    hire March 27, will  continue to be used as the  anniversary
                    date for calculating carry-over vacation.

13. Home Leave:     The  Company  agrees to pay for two  business  or four coach
                    class tickets per anniversary  year for you and each of your
                    immediate  family members  residing in the foreign  location
                    for return to one destination in the U.S.

14. Repatriation:   Upon  termination of your employment  except for termination
                    by United  for cause as  defined in Section 16 or unless you
                    voluntarily  resign prior to the end of this Agreement,  the
                    Company will pay all  repatriation  costs in accordance with
                    United policy to one destination in the U.S.

15. Employee        You acknowledge that you may incur personal  expenses in the
    Receivables:    course of your  employment  with  UGC.  These  expenses  may
                    include,  but are not  limited  to,  personal  phone  calls,
                    personal travel expenses,  travel advances,  and amounts due
                    as a result of the tax equalization  calculation.  You agree
                    that UGC may deduct  expenses  you owe either the Company or
                    UGC from your paycheck at any time during your employment.

                    You also  agree  that if you fail to  return,  or  return in
                    damaged  condition,  any  items  you have  received  for use
                    during your employment with UGC (such as computer equipment,
                    fax machine,  etc.),  that upon separation from UGC the fair
                    market  value of such items may be deducted  from your final
                    paycheck.  Also,  the Company or UGC may pursue  other legal
                    remedies  available to recover the  reasonable  value of any
                    items not returned.

16. Termination:    Although it is not  anticipated,  your  employment  and this
                    Agreement  may be  terminated  before  the end of its stated
                    assignment   length  with  or  without   cause.   Cause  for
                    termination  shall  include but not be limited to violations
                    of Company policy,  unsatisfactory  job performance,  sexual
                    harassment or other workplace misconduct,  misuse of expense
                    account,   falsification  of  Company  records,  or  similar
                    offenses.  Your  employment  and this  Agreement may also be
                    terminated  without  cause for any reason.  In the case of a
                    termination by the Company without cause,  before the end of
                    your  assignment  term,  however,  you will be entitled to a

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<PAGE>
                                                      Extension Letter Agreement
                                                                     John Porter
                                                                    July 7, 2000


                    severance  payment  equal to twelve  (12)  months  salary or
                    salary  through  the end of the  term  of  your  assignment,
                    whichever is less. As a condition of receiving the severance
                    payment,  however,  you  will  be  required  to sign a legal
                    release  giving up your rights to sue United and the company
                    to which you have been  seconded  for any reason  related to
                    your employment and separation from employment.

17. UGC Policies:   The Company may change, at its sole discretion, from time to
                    time, the provisions of benefit plans,  expatriate  policies
                    or other corporate policies.

18. Confidential    You will not, during or after your  employment,  disclose or
    Information:    use for the  benefit of any person or entity  other than UGC
                    or the Company, any UGC or Company confidential  information
                    that you develop or receive during your employment.  UGC and
                    Company  confidential  information  shall  include all trade
                    secrets,  research and development information,  product and
                    marketing plans,  personnel and financial data,  product and
                    service  specifications,   prototypes,   software,   models,
                    customer  lists  and  other   confidential   information  or
                    materials of UGC, the Company, or of others with whom UGC or
                    the  Company  has  a  confidential  relationship.  You  will
                    promptly  return all such  information  and materials to UGC
                    when your employment ends.

19. Severability    In case any one or more of the  provisions of this Agreement
    and Survival    shall be found to be invalid,  illegal or  unenforceable  in
    of Terms:       any respect,  the validity,  legality and  enforceability of
                    the remaining  provisions  contained in this  Agreement will
                    not be affected.  Further,  any provision or portion of this
                    Agreement  found to be invalid,  illegal,  or  unenforceable
                    shall be deemed,  without  further action on the part of you
                    or UGC to be modified, amended and/or limited to the minimum
                    extent  necessary  to render  such  provisions  or  portions
                    thereof valid and enforceable. The provisions of this letter
                    regarding  trade secrets and  confidential  information  and
                    arbitration shall survive the termination of your employment
                    by UGC.

20. Entire          This Agreement  contains the parties' entire  agreement with
    Agreement:      respect to your  expatriate  assignment  and  supersedes any
                    prior written or oral  agreements the parties may have made.
                    This  Agreement  may be amended  only by a written  document
                    signed by you, UGC and the Company.

21. Governing Law:  This   Agreement   and  all   aspects  of  your   employment
                    relationship with UGC are governed by the laws of the United
                    States and the State of Colorado and all disputes concerning
                    same will be resolved in Colorado.

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<PAGE>
                                                      Extension Letter Agreement
                                                                     John Porter
                                                                    July 7, 2000


22. Release:        You   acknowledge   that  you  have  received  any  and  all
                    compensation and payments under the 1995 Agreement.

     If the  above  employment  terms are  satisfactory,  please  indicate  your
acceptance of our offer by signing and returning two executed  originals of this
letter.

     Sincerely,

UNITEDGLOBALCOM, INC.


By: /s/ Michael T. Fries
   -------------------------------------
Its:
    ------------------------------------
Date:
     -----------------------------------


AUSTAR UNITED COMMUNICATIONS LIMITED



By: /s/ Michael T. Fries
   -------------------------------------
Its:
    ------------------------------------
Date:
     -----------------------------------




ACCEPTED and AGREED:


/s/ John C. Porter
---------------------------------------
John Porter

Date: July 25, 2000




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