Nicor Gas Company
                                                        Form 10-K
                                                        Exhibit 4.17


                             Supplemental Indenture


                             DATED FEBRUARY 1, 2001


                          NORTHERN ILLINOIS GAS COMPANY

                                       TO

                          BNY MIDWEST TRUST COMPANY
                 (successor to HARRIS TRUST AND SAVINGS BANK)

                       TRUSTEE UNDER INDENTURE DATED AS OF
                        JANUARY 1, 1954 AND SUPPLEMENTAL
                               INDENTURES THERETO

                              FIRST MORTGAGE BONDS
                      6 5/8% SERIES DUE FEBRUARY 1, 2011

This  instrument  was  prepared  by  George M.   Behrens,   1844  Ferry  Road,
Naperville, Illinois 60563-9600.

Return to:        Nicor Gas Company
                  Attn: Joe Johnson
                  P.O. Box 190
                  Aurora, IL 60507-0190


<PAGE>







THIS   SUPPLEMENTAL INDENTURE,  dated the first day of February,  2001, between
       Northern Illinois Gas Company, a corporation organized and existing under
       the laws of the State of Illinois (hereinafter called the "Company"), and
       BNY Midwest Trust Company, an Illinois trust company, (hereinafter called
       the  "Trustee"),  as successor  Trustee  under an  Indenture  dated as of
       January  1, 1954,  as  supplemented  by  Supplemental  Indentures  dated,
       respectively,  February  9, 1954,  April 1, 1956,  June 1, 1959,  July 1,
       1960, June 1, 1963, July 1, 1963,  August 1, 1964, August 1, 1965, May 1,
       1966,  August 1, 1966,  July 1, 1967,  June 1,  1968,  December  1, 1969,
       August 1, 1970, June 1, 1971, July 1, 1972, July 1, 1973,  April 1, 1975,
       April 30, 1976, April 30, 1976, July 1, 1976, August 1, 1976, December 1,
       1977, January 15, 1979, December 1, 1981, March 1, 1983, October 1, 1984,
       December 1, 1986,  March 15, 1988,  July 1, 1988,  July 1, 1989, July 15,
       1990,  August 15, 1991, July 15, 1992,  February 1, 1993, March 15, 1993,
       May 1, 1993,  July 1, 1993,  August 15, 1994,  October 15, 1995,  May 10,
       1996, August 1, 1996, June 1, 1997, October 15, 1997,  February 15, 1998,
       June 1, 1998 and February 1, 1999,  such Indenture dated as of January 1,
       1954, as so supplemented, being hereinafter called the "Indenture."

Witnesseth:

       Whereas,  the  Trustee  has become  fully  vested  with all the  estates,
authority,  rights,  trusts,  powers, duties and obligations of Harris Trust and
Savings  Bank  under  the  Indenture  pursuant  to  that  certain  Agreement  of
Resignation,  Appointment and Acceptance dated as of January 22, 2001,  attached
hereto as Exhibit A, and Section 17.07 of the Indenture; and

       Whereas,  the  Indenture  provides  for the  issuance  from  time to time
thereunder,  in series,  of bonds of the Company for the purposes and subject to
the limitations therein specified; and

       Whereas, the Company desires, by this Supplemental  Indenture,  to create
an additional series of bonds to be issuable under the Indenture,  such bonds to
be  designated  "First  Mortgage  Bonds,  6 5/8%  Series due  February  1, 2011"
(hereinafter called the "bonds of this Series"), and the terms and provisions to
be contained in the bonds of this Series or to be otherwise  applicable  thereto
to be as set forth in this Supplemental Indenture; and

       Whereas,  the  forms,  respectively,  of the  bonds of this  Series,  and
Trustee's  certificate  to be  endorsed on all bonds of this  Series,  are to be
substantially as follows:


                            (FORM OF FACE OF BOND)

NO. RU                                                                  $




<PAGE>


                          NORTHERN ILLINOIS GAS COMPANY

           First Mortgage Bond, 6 5/8% Series due February 1, 2011

       Northern  Illinois  Gas  Company,  an Illinois  corporation  (hereinafter
called the "Company"), for value received, hereby promises to pay to
                        or registered assigns, the sum of
       Dollars, on the first day of February, 2011, and to pay to the registered
owner  hereof  interest on said sum from the date hereof until said sum shall be
paid, at the rate of six and five-eighths per centum (6 5/8%) per annum, payable
semiannually  on the first day of  February  and the first day of August in each
year.  Both the  principal  of and the interest on this bond shall be payable at
the office or agency of the Company in the City of Chicago,  State of  Illinois,
or,  at the  option  of the  registered  owner,  at the  office or agency of the
Company in the Borough of Manhattan, The City and State of New York, in any coin
or  currency  of the United  States of  America  which at the time of payment is
legal tender for the payment of public and private  debts.  Any  installment  of
interest on the bonds may, at the Company's  option,  be paid by mailing  checks
for such interest  payable to or upon the written  order of the person  entitled
thereto to the address of such person as it appears on the registration books.

       So long as there is no  existing  default in the  payment of  interest on
this bond, the interest so payable on any interest  payment date will be paid to
the person in whose name this bond is  registered  on the January 15 or the July
15 (whether or not a business  day),  as the case may be,  next  preceding  such
interest  payment  date.  If and to the extent that the Company shall default in
the  payment of interest  due on such  interest  payment  date,  such  defaulted
interest  shall be paid to the person in whose name this bond is  registered  on
the record  date  fixed,  in  advance,  by the  Company  for the payment of such
defaulted interest.

       Additional provisions of this bond are set forth on the reverse hereof.

       This bond shall not be  entitled  to any  security  or benefit  under the
Indenture or be valid or become  obligatory  for any purpose unless and until it
shall have been authenticated by the execution by the Trustee,  or its successor
in trust under the Indenture, of the certificate endorsed hereon.

       In Witness Whereof, Northern Illinois Gas Company has caused this bond to
be  executed  in its  name  by its  Chairman,  President,  or a Vice  President,
manually or by  facsimile  signature,  and has caused its  corporate  seal to be
impressed  hereon  or a  facsimile  thereof  to be  imprinted  hereon  and to be
attested by its Secretary or its Assistant  Secretary,  manually or by facsimile
signature.

Dated

                                                 NORTHERN ILLINOIS GAS COMPANY

                                                 By
                                                       President
Attest:

           Secretary



<PAGE>




              (FORM OF TRUSTEE'S CERTIFICATE OF AUTHENTICATION)

       This bond is one of the bonds of the series designated therein,  referred
to and described in the within-mentioned  Supplemental  Indenture dated February
1, 2001.

BNY MIDWEST TRUST COMPANY,
Trustee

By
     Authorized Officer

                         (Form of Reverse Side of Bond)

       This  bond is one,  of the  series  hereinafter  specified,  of the bonds
issued and to be issued in series from time to time under and in accordance with
and secured by an Indenture  dated as of January 1, 1954,  to BNY Midwest  Trust
Company, as Trustee, as supplemented by certain indentures supplemental thereto,
executed and delivered to the Trustee;  and this bond is one of a series of such
bonds,  designated  "Northern  Illinois Gas Company First Mortgage Bonds, 6 5/8%
Series due  February  1,  2011"  (herein  called  "bonds of this  Series"),  the
issuance of which is provided for by a Supplemental  Indenture dated February 1,
2001 (hereinafter called the "Supplemental  Indenture"),  executed and delivered
by the Company to the Trustee. The term "Indenture",  as hereinafter used, means
said  Indenture  dated as of January 1, 1954,  and all  indentures  supplemental
thereto from time to time in effect.  Reference is made to the  Indenture  for a
description of the property mortgaged and pledged,  the nature and extent of the
security,  the rights of the holders and registered owners of said bonds, of the
Company  and of the  Trustee  in  respect  of the  security,  and the  terms and
conditions governing the issuance and security of said bonds.

       With the  consent of the Company  and to the extent  permitted  by and as
provided in the Indenture,  modifications  or alterations of the Indenture or of
any supplemental  indenture and of the rights and obligations of the Company and
of the holders and  registered  owners of the bonds may be made,  and compliance
with any  provision of the  Indenture or of any  supplemental  indenture  may be
waived, by the affirmative vote of the holders and registered owners of not less
than sixty-six and  two-thirds  per centum (66 2/3%) in principal  amount of the
bonds then outstanding  under the Indenture,  and by the affirmative vote of the
holders and  registered  owners of not less than  sixty-six and  two-thirds  per
centum (66 2/3%) in principal amount of the bonds of any series then outstanding
under the Indenture and affected by such modification or alteration, in case one
or more but less than all of the  series  of bonds  then  outstanding  under the
Indenture are so affected,  but in any case excluding  bonds  disqualified  from
voting by reason of the Company's interest therein as provided in the Indenture;
subject,  however,  to the  condition,  among  other  conditions  stated  in the
Indenture,  that no such  modification or alteration shall be made which,  among
other  things,  will permit the extension of the time or times of payment of the
principal  of or the  interest  or the  premium,  if any,  on this bond,  or the
reduction  in the  principal  amount  hereof or in the rate of  interest  or the
amount of any premium hereon, or any other  modification in the terms of payment
of  such   principal,   interest  or   premium,   which  terms  of  payment  are
unconditional, or, otherwise than as permitted by the Indenture, the creation of
any lien  ranking  prior to or on a parity with the lien of the  Indenture  with
respect to any of the  mortgaged  property,  all as more fully  provided  in the
Indenture.

       The bonds of this Series may be called for redemption by the Company,  as
a whole at any time or in part from time to time, at a redemption price equal to
the greater of (i) 100% of the  principal  amount of the bonds of this Series to
be  redeemed or (ii) the sum of the present  values of the  remaining  scheduled
payments of principal and interest thereon (exclusive of interest accrued to the
date of redemption) discounted, at the then current Treasury Rate (as defined in
the Supplemental Indenture) plus 25 basis points, to the date of redemption on a
semiannual  basis  (assuming a 360-day year  consisting of twelve 30-day months)
plus in each case,  accrued and unpaid  interest on the  principal  amount being
redeemed to the date of redemption.

       Notice of each  redemption  shall be mailed to all registered  owners not
less than thirty nor more than forty-five days before the redemption date.

       In case of certain  completed  defaults  specified in the Indenture,  the
principal  of this bond may be  declared  or may become  due and  payable in the
manner and with the effect provided in the Indenture.

       No  recourse  shall be had for the  payment  of the  principal  of or the
interest or the premium, if any, on this bond, or for any claim based hereon, or
otherwise in respect hereof or of the Indenture, to or against any incorporator,
stockholder,  officer or director, past, present or future, of the Company or of
any predecessor or successor corporation, either directly or through the Company
or such predecessor or successor corporation,  under any constitution or statute
or  rule  of  law,  or by the  enforcement  of any  assessment  or  penalty,  or
otherwise,  all such  liability of  incorporators,  stockholders,  directors and
officers  being  waived  and  released  by the  registered  owner  hereof by the
acceptance of this bond and being  likewise  waived and released by the terms of
the Indenture, all as more fully provided therein.

       This bond is transferable by the registered owner hereof, in person or by
duly authorized attorney,  at the office or agency of the Company in the City of
Chicago,  State of Illinois,  or, at the option of the registered  owner, at the
office or agency of the Company in the Borough of Manhattan,  The City and State
of New York,  upon surrender and  cancellation of this bond; and thereupon a new
registered bond or bonds without coupons of the same aggregate  principal amount
and series  will,  upon the payment of any  transfer  tax or taxes  payable,  be
issued to the transferee in exchange herefor.  The Company shall not be required
to  exchange  or  transfer  this bond if this bond or a portion  hereof has been
selected for redemption.


<PAGE>




                              (END OF BOND FORM)

and

       Whereas,  all  acts  and  things  necessary  to  make  this  Supplemental
Indenture,  when  duly  executed  and  delivered,  a valid,  binding  and  legal
instrument in accordance with its terms and for the purposes  herein  expressed,
have  been  done  and  performed,   and  the  execution  and  delivery  of  this
Supplemental Indenture have in all respects been duly authorized;

       Now,  Therefore,  in  consideration of the premises and of the sum of one
dollar  paid by the  Trustee to the  Company,  and for other  good and  valuable
considerations,  the receipt of which is hereby acknowledged, for the purpose of
securing the due and punctual  payment of the  principal of and the interest and
premium, if any, on all bonds which shall be issued under the Indenture, and for
the purpose of securing  the  faithful  performance  and  observance  of all the
covenants  and  conditions  set  forth in the  Indenture  and in all  indentures
supplemental thereto, the Company by these presents does grant,  bargain,  sell,
transfer,  assign, pledge,  mortgage,  warrant and convey unto BNY Midwest Trust
Company,  as  Trustee,  and its  successor  or  successors  in the trust  hereby
created, all property, real and personal (other than property expressly excepted
from the lien and  operation  of the  Indenture),  which,  at the actual date of
execution and delivery of this  Supplemental  Indenture,  is solely used or held
for use in the  operation  by the Company of its gas  utility  system and in the
conduct of its gas utility business and all property, real and personal, used or
useful in the gas utility business (other than property  expressly excepted from
the lien and  operation  of the  Indenture)  acquired by the  Company  after the
actual date of execution and delivery of this Supplemental Indenture or (subject
to  the  provisions  of  Section  16.03  of  the  Indenture)  by  any  successor
corporation  after such execution and delivery,  and it is further agreed by and
between the Company and the Trustee as follows:

                                    ARTICLE I

                              Bonds of this Series

       Section 1. The bonds of this Series shall,  as hereinbefore  recited,  be
designated as the Company's "First Mortgage Bonds, 6 5/8% Series due February 1,
2011." The bonds of this Series  which may be issued and  outstanding  shall not
exceed  $75,000,000 in aggregate  principal  amount,  exclusive of bonds of such
series authenticated and delivered pursuant to the provisions of Section 4.12 of
the Indenture.

       Section 2. The bonds of this Series  shall be  registered  bonds  without
coupons,  and the  form of  such  bonds,  and of the  Trustee's  certificate  of
authentication   to  be  endorsed  on  all  bonds  of  this  Series,   shall  be
substantially as hereinbefore recited, respectively.

       Section 3. The bonds of this Series  shall be issued in the  denomination
of $1,000 each and in such multiple or multiples  thereof as shall be determined
and  authorized  by the Board of  Directors  of the Company or by any officer or
officers  of the  Company  authorized  by the  Board of  Directors  to make such
determination,  the  authorization  of  the  denomination  of  any  bond  to  be
conclusively  evidenced by the execution  thereof on behalf of the Company.  The
bonds of this Series shall be numbered,  RU-1 and consecutively  upwards,  or in
such other appropriate manner as shall be determined and authorized by the Board
of Directors of the Company.

       All bonds of this Series  shall be dated  February  1, 2001,  except that
each bond  issued on or after the first  payment of  interest  thereon  shall be
dated as of the date of the  interest  payment  date  thereof to which  interest
shall  have been paid on the bonds of such  series  next  preceding  the date of
issue,  unless issued on an interest  payment date to which  interest shall have
been so paid,  in which event such bonds shall be dated as of the date of issue;
provided,  however, that bonds issued on or after January 15 and before the next
succeeding  February 1 or on or after  July 15 and  before  the next  succeeding
August 1 shall be dated the next  succeeding  interest  payment date if interest
shall  have  been  paid to such  date.  All bonds of this  Series  shall  mature
February  1, 2011 and shall bear  interest at the rate of 6 5/8% per annum until
the principal  thereof shall be paid.  Such interest  shall be calculated on the
basis of a 360-day year  consisting of twelve 30-day months and shall be payable
semiannually  on the first day of  February  and the first day of August in each
year. So long as there is no existing  default in the payment of interest on the
bonds of this Series, such interest shall be payable to the person in whose name
each such bond is  registered on the January 15 or the July 15 (whether or not a
business  day),  as the case may be,  next  preceding  the  respective  interest
payment dates;  provided,  however,  if and to the extent that the Company shall
default in the payment of  interest  due on such  interest  payment  date,  such
defaulted  interest  shall be paid to the person in whose name each such bond is
registered on the record date fixed, in advance,  by the Company for the payment
of such defaulted interest.

       The  principal of and interest and premium,  if any, on the bonds of this
Series shall be payable in any coin or currency of the United  States of America
which at the time of  payment  is legal  tender  for the  payment  of public and
private  debts,  and shall be payable at the office or agency of the  Company in
the City of  Chicago,  State of  Illinois,  or, at the option of the  registered
owner,  at the office or agency of the Company in the Borough of Manhattan,  The
City and State of New York. Any installment of interest on the bonds may, at the
Company's option, be paid by mailing checks for such interest payable to or upon
the written order of the person  entitled  thereto to the address of such person
as it appears  on the  registration  books.  The bonds of this  Series  shall be
registrable,  transferable  and  exchangeable in the manner provided in Sections
4.08 and 4.09 of the Indenture, at either of such offices or agencies.

       Section 4. The bonds of this  Series,  upon the  mailing of notice and in
the manner  provided in Section 7.01 of the Indenture  (except that no published
notice  shall be  required  for the bonds of this  Series)  and with the  effect
provided  in Section  7.02  thereof,  shall be  redeemable  at the option of the
Company,  as a whole at any time or in part from time to time,  at a  redemption
price equal to the greater of (i) 100% of the  principal  amount of the bonds of
this  Series  to be  redeemed  or (ii)  the  sum of the  present  values  of the
remaining  scheduled  payments of principal and interest  thereon  (exclusive of
interest  accrued to the date of  redemption)  discounted,  at the then  current
Treasury  Rate plus 25 basis  points,  to the date of redemption on a semiannual
basis  (assuming a 360-day year consisting of twelve 30-day months) plus in each
case,  accrued and unpaid interest on the principal amount being redeemed to the
date of redemption.

       "Treasury Rate" means, for any redemption date, (i) the yield,  under the
heading  which  represents  the  average  for the  immediately  preceding  week,
appearing  in  the  most  recently  published   statistical  release  designated
"H.15(519)" or any successor  publication which is published weekly by the Board
of  Governors  of the Federal  Reserve  System and which  establishes  yields on
actively traded United States Treasury  securities adjusted to constant maturity
under the caption "Treasury Constant Maturities," for the maturity corresponding
to the  Comparable  Treasury Issue (if no maturity is within three months before
or after the  remaining  term of the bonds of this  Series,  yields  for the two
published maturities most closely corresponding to the Comparable Treasury Issue
shall be determined and the Treasury Rate shall be  interpolated or extrapolated
from such  yields on a straight  line basis,  rounding to the nearest  month) or
(ii) if such release (or any successor release) is not published during the week
preceding  the  calculation  date or does not contain such yields,  the rate per
annum equal to the  semiannual  equivalent  yield to maturity of the  Comparable
Treasury  Issue,  calculated  using a price for the  Comparable  Treasury  Issue
(expressed  as a percentage of its  principal  amount)  equal to the  Comparable
Treasury Price.  The Treasury Rate shall be calculated on the third Business Day
preceding the redemption date.

       "Business  Day" means,  for the purpose of this  Section 4, any day other
than a Saturday or Sunday and other than a day on which banking  institutions in
Chicago,  Illinois, or New York, New York, are authorized or obligated by law or
executive order to close.

       "Comparable  Treasury  Issue" means the United States  Treasury  security
selected by an Independent  Investment Banker as having a maturity comparable to
the  remaining  term of the bonds of this  Series to be  redeemed  that would be
utilized,  at the time of selection and in accordance  with customary  financial
practice,  in pricing new issues of  corporate  debt  securities  of  comparable
maturity to the remaining term of the bonds of this Series.

       "Comparable  Treasury Price" means the average of two Reference  Treasury
Dealer Quotations obtained with respect to any redemption date.

       "Independent Investment Banker" means ABN AMRO Incorporated or one of the
Reference  Treasury Dealers appointed by the Trustee after consultation with the
Company.

       "Reference  Treasury  Dealer"  means  each of ABN AMRO  Incorporated  and
Salomon Smith Barney Inc. and their successors;  provided,  however, that if any
of the foregoing or their  successors  shall cease to be a primary United States
government  securities  dealer (a "Primary Treasury  Dealer"),  the Company will
substitute  for it  another  nationally  recognized  investment  bank  that is a
Primary Treasury Dealer.

       "Reference  Treasury  Dealer  Quotations"  means,  with  respect  to each
Reference Treasury Dealer and any redemption date, the average, as determined by
the  Independent  Investment  Banker,  of the  bid  and  asked  prices  for  the
Comparable  Treasury  Issue  (expressed  in  each  case as a  percentage  of its
principal amount) quoted in writing to the Independent Investment Banker at 5:00
p.m., New York City time, on the third  Business Day preceding  such  redemption
date.

       Section  5. No  sinking  fund is to be  provided  for the  bonds  of this
Series.


<PAGE>


                                   ARTICLE II

                            Miscellaneous Provisions

       Section 1. This Supplemental Indenture is executed by the Company and the
Trustee  pursuant to  provisions  of Section 4.02 of the Indenture and the terms
and  conditions  hereof shall be deemed to be a part of the terms and conditions
of the  Indenture  for  any and  all  purposes.  The  Indenture,  as  heretofore
supplemented  and as  supplemented  by this  Supplemental  Indenture,  is in all
respects ratified and confirmed.

       Section 2. This  Supplemental  Indenture  shall bind and,  subject to the
provisions  of  Article  XVI of the  Indenture,  inure  to  the  benefit  of the
respective successors and assigns of the parties hereto.

       Section 3.  Although  this  Supplemental  Indenture is dated  February 1,
2001, it shall be effective only from and after the actual time of its execution
and  delivery  by the Company  and the  Trustee on the date  indicated  by their
respective acknowledgments hereto annexed.

       Section 4. This Supplemental Indenture may be simultaneously  executed in
any number of counterparts,  and all such  counterparts  executed and delivered,
each as an original, shall constitute but one and the same instrument.

       In Witness  Whereof,  Northern  Illinois  Gas  Company  has  caused  this
Supplemental  Indenture  to be  executed  in its name by its  President,  a Vice
President,  or  Treasurer,  and its  corporate  seal to be hereunto  affixed and
attested by its  Secretary or its  Assistant  Secretary,  and BNY Midwest  Trust
Company, as Trustee under the Indenture,  has caused this Supplemental Indenture
to be executed in its name by one of its Assistant Vice Presidents, and its seal
to be hereunto affixed and attested by one of its Assistant Secretaries,  all as
of the day and year first above written.

NORTHERN ILLINOIS GAS COMPANY

By
        GEORGE M. BEHRENS
        Vice President and Treasurer


                                           Attest:
                                                    ALEXANDER C. ALLISON
                                                     Assistant Secretary

BNY MIDWEST TRUST COMPANY
  as Trustee

By
        D.G. DONOVAN
        Assistant Vice President

                                           Attest:
                                                       C. POTTER
                                                    Assistant Secretary


<PAGE>



State of Illinois
County of DuPage}         ss:

       I, Cathy A. Gengler,  a Notary Public in the State  aforesaid,  Do Hereby
Certify  that  George M.  Behrens,  Vice  President  and  Treasurer  of Northern
Illinois Gas Company, an Illinois  corporation,  one of the parties described in
and which executed the foregoing instrument, and Alexander C. Allison, Assistant
Secretary of said  corporation,  who are both  personally  known to me to be the
same persons whose names are subscribed to the foregoing instrument as such Vice
President and Treasurer and Assistant Secretary,  respectively, and who are both
personally  known to me to be Vice  President  and  Treasurer  and the Assistant
Secretary,  respectively,  of said  corporation,  appeared before me this day in
person  and  severally  acknowledged  that they  signed,  sealed,  executed  and
delivered said instrument as their free and voluntary act as such Vice President
and Treasurer and Assistant Secretary, respectively, of said corporation, and as
the free  and  voluntary  act of said  corporation,  for the  uses and  purposes
therein set forth.

       Given under my hand and notarial seal this day of A.D.


                                                          Notary Public


My Commission expires August 4, 2001



<PAGE>


State of Illinois
County of Cook}   ss:

       I, Linda E. Garcia, a Notary Public in and for said County,  in the State
aforesaid,  Do Hereby Certify that D.G. Donovan,  an Assistant Vice President of
BNY  Midwest  Trust  Company,  an  Illinois  trust  company,  one of the parties
described in and which  executed the  foregoing  instrument,  and C. Potter,  an
Assistant  Secretary of said trust company,  who are both personally known to me
to be the same persons whose names are subscribed to the foregoing instrument as
such Assistant Vice President and Assistant Secretary, respectively, and who are
both  personally  known to me to be an Assistant Vice President and an Assistant
Secretary,  respectively,  of said trust company, appeared before me this day in
person  and  severally  acknowledged  that they  signed,  sealed,  executed  and
delivered said instrument as their free and voluntary act as such Assistant Vice
President and Assistant Secretary,  respectively,  of said trust company, and as
the free and  voluntary  act of said trust  company,  for the uses and  purposes
therein set forth.

       Given under my hand and notarial seal this day of A.D.


                                                 Notary Public


My Commission expires September 23, 2002


<PAGE>




                                 RECORDING DATA

       This Supplemental  Indenture was recorded on January 29th and 30th, 2001,
in the  office of the  Recorder  of Deeds in  certain  counties  in the State of
Illinois, as follows:

         County             Book              Page          Document No.

     Adams
     Boone
     Bureau
     Carroll
     Champaign
     Cook
     DeKalb
     DeWitt
     DuPage
     Ford
     Grundy
     Hancock
     Henderson
     Henry
     Iroquois
     Jo Daviess
     Kane
     Kankakee
     Kendall
     Lake
     La Salle
     Lee
     Livingston
     McHenry
     McLean
     Mercer
     Ogle
     Platt
     Pike
     Rock Island
     Stephenson
     Tazewell
     Vermillon
     Whiteside
     Will
     Winnebago
     Woodford

<PAGE>









                                                                       Exhibit A



AGREEMENT OF RESIGNATION,  APPOINTMENT  AND ACCEPTANCE,  dated as of January 22,
2001 by and among Northern  Illinois Gas Company,  a corporation  duly organized
and  existing  under the laws of the State of Illinois  (the  "Issuer"),  Harris
Trust and Savings Bank, an Illinois banking  corporation  ("Prior  Trustee") and
BNY Midwest Trust Company, a trust corporation duly organized and existing under
the laws of the State of Illinois ("Successor Trustee").

                                    RECITALS:

WHEREAS,  Commonwealth Edison Company and Continental Illinois National Bank and
Trust Company of Chicago entered into an indenture, dated as of January 1, 1954,
as amended and supplemented (the  "Indenture")  which Indenture was adopted by a
predecessor of the Issuer pursuant to an Indenture of Adoption dated February 1,
1954;

WHEREAS,  the Indenture  provides for the issuance from time to time thereunder,
in series, of bonds of the Issuer for its lawful corporate purposes; and

WHEREAS,  the  Prior  Trustee  has been  acting  as  Trustee,  paying  agent and
registrar under the Indenture; and

WHEREAS,  the Issuer  desires to appoint  Successor  Trustee as Trustee,  paying
agent and  registrar  to  succeed  Prior  Trustee in such  capacities  under the
Indenture; and

WHEREAS,  Successor  Trustee is willing to accept such  appointment as successor
Trustee, paying agent and registrar under the Indenture;

NOW,  THEREFORE,  the Issuer,  Prior Trustee and Successor  Trustee,  for and in
consideration  of the  premises of other good and  valuable  consideration,  the
receipt and  sufficiency  of which are hereby  acknowledged,  hereby consent and
agree as follows:


                                    ARTICLE I

                                THE PRIOR TRUSTEE

SECTION 1.01 Pursuant to Section 17.06 of the  Indenture,  Prior Trustee  hereby
notifies the Issuer that the Prior  Trustee is  resigning  as Trustee  under the
Indenture effective as of January 22, 2001 (the "Effective Date").

SECTION 1.02 Prior Trustee hereby assigns,  transfers,  delivers and confirms to
Successor  Trustee all right,  title and interest of Prior Trustee in and to the
trusts of the Trustee under the Indenture and all the rights,  powers and trusts
of the Trustee under the Indenture. Prior Trustee shall execute and deliver such
further  instruments and shall do such other things as Successor  Trustee or the
Issuer may reasonably require so as to more fully and certainly vest and confirm
in  Successor  Trustee  all the  rights,  powers  and  trusts  hereby  assigned,
transferred,  delivered  and confirmed to Successor  Trustee as Trustee,  paying
agent and registrar.

SECTION 1.03 Promptly  after the execution and delivery of this  Agreement,  the
Prior Trustee shall cause notice of its resignation  effected hereby to be given
as is required pursuant to Section 17.06 of the Indenture.



<PAGE>



                                     ARTICLE II

                                     THE ISSUER

SECTION  2.01 The Issuer  hereby  accepts the  resignation  of Prior  Trustee as
Trustee, paying agent and registrar under the Indenture.

SECTION 2.02 All  conditions  relating to the  appointment  of BNY Midwest Trust
Company as Successor  Trustee,  paying agent and  registrar  under the Indenture
have been met by the Issuer, and the Issuer hereby appoints Successor Trustee as
Trustee,  paying agent and registrar  under the Indenture with like effect as if
originally named as Trustee, paying agent and registrar in the Indenture.

SECTION 2.03 The Issuer agrees to give,  or cause to be given,  prompt notice of
the  appointment of the Successor  Trustee to the bondholders in accordance with
Section 17.07 of the Indenture.

                                   ARTICLE III

                              THE SUCCESSOR TRUSTEE

SECTION 3.01 Successor  Trustee hereby  represents and warrants to Prior Trustee
and to the Issuer that  Successor  Trustee is qualified  and eligible  under the
provisions of Section 17.06 of the Indenture to be appointed  successor  Trustee
and that it has power and authority to execute and deliver this Agreement and to
perform its obligations hereunder, and all such action has been duly and validly
authorized by all necessary proceedings on its part.

SECTION 3.02  Successor  Trustee  hereby  accepts its  appointment  as successor
Trustee,  paying agent and registrar under the Indenture and accepts the rights,
powers,  duties and  obligations  of Prior Trustee as Trustee,  paying agent and
registrar under the Indenture,  upon the terms and conditions set forth therein,
with like effect as if originally  named as Trustee,  paying agent and registrar
under the Indenture.


                                     ARTICLE IV

                                  MISCELLANEOUS

SECTION 4.01 This  Agreement and the  resignation,  appointment  and  acceptance
effected  hereby  shall  be  effective  as of the  opening  of  business  on the
Effective Date.

SECTION 4.02 This  Agreement  shall be governed by and  construed in  accordance
with the laws of the Indenture.

SECTION 4.03 This Agreement may be executed in any number of  counterparts  each
of which shall be an original,  but such counterparts shall together  constitute
but one and the same instrument.




<PAGE>



IN WITNESS WHEREOF, the parties hereto have caused this Agreement of Resignation
Appointment  and Acceptance to be duly executed and  acknowledged  all as of the
day and year first above written.


                                          Northern Illinois Gas Company
                                                 as Issuer

                                          By: ____________________________
                                          Name:
                                          Title:




                                           Harris Trust and Savings Bank,
                                             as Prior Trustee


                                          By: ____________________________
                                          Name:  F. A. Pierson
                                          Title: Vice President




                                          BNY Midwest Trust Company,
                                             as Successor Trustee


                                          By: ____________________________
                                          Name:  D. G. Donovan
                                          Title: Assistant Vice President





<PAGE>






STATE OF ILLINOIS }
                        }     ss.
COUNTY OF DUPAGE  }


      On  this  22nd  day  of  January,  2001,  before  me  personally  appeared
__________________,  _____________________  of Northern  Illinois  Gas  Company,
known to me to be the person who executed the within instrument on behalf of the
corporation therein named and acknowledged to me that such corporation  executed
the within  instrument  pursuant to its by-laws or a resolution  of its board of
directors.



                               Name:
                               Notary Public, DuPage County, State of Illinois


(Seal)

My Commission expires on




<PAGE>




STATE OF ILLINOIS}
                        }     ss.
COUNTY OF COOK}


On this 22nd day of January,  2001, before me personally appeared F. A. Pierson,
Vice  President of Harris Trust and Savings  Bank,  known to me to be the person
who executed the within  instrument on behalf of the  corporation  therein named
and  acknowledged  to me that such  corporation  executed the within  instrument
pursuant to its by-laws or a resolution of its board of directors.



                                  Name: Linda Ellen Garcia
                                  Notary Public, Cook County, State of Illinois


(Seal)

My Commission expires on September 23, 2002




STATE OF ILLINOIS}
                        }     ss.
COUNTY OF COOK}


On this 22nd day of January,  2001, before me personally appeared D. G. Donovan,
Assistant  Vice  President of BNY Midwest Trust  Company,  known to me to be the
person who executed the within  instrument on behalf of the corporation  therein
named  and  acknowledged  to  me  that  such  corporation  executed  the  within
instrument pursuant to its by-laws or a resolution of its board of directors.



                                  Name: Linda Ellen Garcia
                                  Notary Public, Cook County, State of Illinois


(Seal)

My Commission expires on September 23, 2002