<PAGE>

                                                                     Exhibit 4.3

================================================================================

                          SECOND SUPPLEMENTAL INDENTURE

                          dated as of ___________, 2002

                                       to

                                 TRUST INDENTURE

                          dated as of October 23, 2001

                                     between

                                ELWOOD ENERGY LLC

                                       and

                             BANK ONE TRUST COMPANY,
                        NATIONAL ASSOCIATION, as Trustee

================================================================================
<PAGE>

      SECOND SUPPLEMENTAL INDENTURE, dated as of ___________, 2002 (this "Second
Supplemental Indenture"), to the Trust Indenture, dated as of October 23, 2001
(the "Original Indenture", and, together with the First Supplemental Indenture
dated October 23, 2001, the "Indenture"), between ELWOOD ENERGY LLC, a Delaware
limited liability company (together with its successors and assigns, the
"Issuer") and BANK ONE TRUST COMPANY, NATIONAL ASSOCIATION, a national banking
corporation (the "Trustee").

      WHEREAS, the Issuer and the Trustee have heretofore executed and delivered
the Original Indenture to provide for the issuance from time to time of Bonds
(as defined in the Original Indenture) of the Issuer, to be issued in one or
more series;

      WHEREAS, the Issuer has filed the Exchange Offer Registration Statement
and completed the Exchange Offer, as contemplated by the Registration Rights
Agreement;

      WHEREAS, the holders of $________________ in initial principal amount of
the Initial Bonds have accepted the Exchange Offer; and

      WHEREAS, all action on the part of the Issuer necessary to authorize the
issuance of the Exchange Bonds has been taken.

      NOW, THEREFORE, THIS SECOND SUPPLEMENTAL INDENTURE WITNESSETH:

      The parties hereto hereby agree as follows:

                                    ARTICLE I

                                   DEFINITIONS

      (a) Capitalized terms used herein and not otherwise defined herein shall
have the respective meanings ascribed thereto in the Indenture.

      (b) The rules of interpretation set forth in the Original Indenture shall
be applied hereto as if set forth in full herein.

                                   ARTICLE II

                               THE EXCHANGE BONDS

      SECTION 2.1. Issuance of the Exchange Bonds. Upon receipt of an
authentication order in accordance with Section 2.4 of the Original Indenture,
the Trustee shall authenticate an Unrestricted Global Bond in the form of
Exhibit A and having a stated principal amount of $____________ representing the
Exchange Bonds.


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<PAGE>

      SECTION 2.2. Reduction of Aggregate Principal Amount of Initial Bonds. The
Trustee shall cause the stated principal amount of the Restricted Global Bond(s)
representing the Initial Bonds to be reduced to $___________.

      SECTION 2.3. Credit for Prior Payments. The principal amounts set forth in
Sections 2.1 and 2.2 are stated in terms of the applicable issuance amount of
the Initial Bonds for ease of computation. All payments of principal and
interest made on Initial Bonds being exchanged for Exchange Bonds on or before
the date of authentication of the Exchange Bonds shall be credited against
amounts payable under the Exchange Bonds.

                                   ARTICLE III

                                  MISCELLANEOUS

      SECTION 3.1. Execution of Supplemental Indenture. This Second Supplemental
Indenture is executed and shall be construed as an indenture supplemental to the
Original Indenture and, as provided in the Original Indenture, this Second
Supplemental Indenture forms a part thereof.

      SECTION 3.2. Concerning the Trustee. The recitals contained herein and in
the Bonds of the series created hereby, except with respect to the Trustee's
certificates of authentication, shall be taken as the statements of the Issuer,
and the Trustee assumes no responsibility for the correctness of the same. The
Trustee makes no representations as to the validity or sufficiency of this
Second Supplemental Indenture or of the Bonds of the series created hereby.

      SECTION 3.3. Counterparts. This Second Supplemental Indenture may be
executed in any number of counterparts, each of which when so executed shall be
deemed to be an original, but all such counterparts shall together constitute
but one and the same instrument.

      SECTION 3.4. Governing Law. THIS SECOND SUPPLEMENTAL INDENTURE SHALL BE
GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW
YORK.

         [THE REMAINDER OF THIS PAGE HAS INTENTIONALLY BEEN LEFT BLANK.]


                                       2
<PAGE>

      IN WITNESS WHEREOF, the parties have caused this Second Supplemental
Indenture to be duly executed by their respective officers thereunto duly
authorized as of the day and year first above written.

                                ELWOOD ENERGY LLC

                                By:
                                   --------------------------------------
                                   Name:
                                   Title:


                                BANK ONE TRUST COMPANY, NATIONAL ASSOCIATION,
                                as Trustee

                                By:
                                   --------------------------------------
                                   Name:
                                   Title:


                                       3
<PAGE>

EXHIBIT A

                                [Form of face of
                      8.159% Senior Secured Bonds due 2026]

                                ELWOOD ENERGY LLC
                      8.159% SENIOR SECURED BONDS DUE 2026

THIS BOND IS A GLOBAL BOND WITHIN THE MEANING OF THE INDENTURE HEREINAFTER
REFERRED TO. THIS GLOBAL BOND IS HELD BY THE REGISTERED DEPOSITARY (AS DEFINED
IN THE INDENTURE GOVERNING THIS BOND) OR ITS NOMINEE IN CUSTODY FOR THE BENEFIT
OF THE BENEFICIAL OWNERS HEREOF, AND IS NOT TRANSFERABLE TO ANY PERSON UNDER ANY
CIRCUMSTANCES EXCEPT THAT (I) THE TRUSTEE MAY MAKE SUCH NOTATIONS HEREON AS MAY
BE REQUIRED BY THE INDENTURE, (II) THIS GLOBAL BOND MAY BE EXCHANGED IN WHOLE
BUT NOT IN PART PURSUANT TO SECTION 2.9(a) OF THE INDENTURE, (III) THIS GLOBAL
BOND MAY BE DELIVERED TO THE TRUSTEE FOR CANCELLATION PURSUANT TO SECTION 2.13
OF THE INDENTURE AND (IV) THIS GLOBAL BOND MAY BE TRANSFERRED TO A SUCCESSOR
REGISTERED DEPOSITARY WITH THE PRIOR WRITTEN CONSENT OF THE ISSUER

No. R-2

CUSIP NUMBER:                                        ____________

PRINCIPAL AMOUNT:                                    $___________

FINAL BOND PAYMENT DATE:                             July 5, 2026

ISSUE DATE:                                          ____________

REGISTERED HOLDER:                                   Cede & Co.

INTEREST RATE:                                       8.159%

      ELWOOD ENERGY LLC, a Delaware limited liability company (hereinafter
called the "Issuer"), which term includes any successor or assign under the
Indenture referred to below), for value received hereby promises to pay to CEDE
& CO., or its registered assigns, the outstanding principal amount hereof, such
payment to be made in semiannual installments on January 5 and July 5 of each
year (commencing January 5, 2002) and ending on the final Bond Payment Date set
forth above, each such installment to be in an amount equal to the principal


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<PAGE>

amount hereof multiplied by the percentage set forth opposite the applicable
payment date in the table set forth on Annex A attached hereto (provided that
the portion of the principal amount remaining unpaid on the final Bond Payment
Date, together with all interest accrued thereon, shall in any and all cases be
due and payable on the final Bond Payment Date), and to pay interest on the
unpaid portion of the Principal Amount at the interest rate set forth above from
the most recent Bond Payment Date to which interest has been paid or duly
provided for or, if no interest has been paid or duly provided for, from the
issue date set forth above, semiannually on January 5 and July 5 in each year
(commencing January 5, 2002) until the principal amount is paid in full or
payment thereof is duly provided for. Any installment of principal and, to the
extent permitted by applicable law, any payment of interest not punctually paid
or duly provided for shall continue to bear interest at a rate equal to the
interest rate set forth above. The principal and interest so payable, and
punctually paid or duly provided for, at any Bond Payment Date shall, as
provided in the Indenture, be paid to the Person in whose name this Bond (or one
or more Predecessor Bonds) is registered in the Security Register at the close
of business on the Regular Record Date for such payment of principal and
interest, which shall be the 15th day (whether or not a Business Day) next
preceding such Bond Payment Date. Any such principal and interest that is
payable, but is not so punctually paid or duly provided for at any Bond Payment
Date, shall forthwith cease to be payable to the Holder hereof on such Regular
Record Date, and such Overdue Interest or Overdue Principal may be paid to the
Person in whose name this Bond (or one or more Predecessor Bonds) is registered
at the close of business on a Special Record Date for the payment of such
Overdue Principal and Overdue Interest (together with any other amounts payable
with respect to such Overdue Principal and Overdue Interest), to be fixed by the
Trustee, notice of which shall be given to the Holder hereof not less than 10
days prior to such Special Record Date, or may be paid at any time in any other
lawful manner not inconsistent with the requirements of any securities exchange
on which this Bond may be listed, and upon such notice as may be required by
such exchange, all as more fully provided in the Indenture. Payments of
principal of and interest on this Bond shall be made (i) if the Issuer so
elects, by check mailed to the Holder of this Bond at his or her registered
address or (ii) otherwise, at the Place of Payment; provided that the final
installment of principal payable with respect to this Bond shall be made as
provided in Section 6.5 of the Indenture (in the event this Bond is redeemed) or
shall be made upon presentation and surrender of this Bond at the Place of
Payment. All payments in respect of this Bond shall be made in such coin or
currency of the United States of America as at the time of payment is legal
tender for payment of debts.

      Whenever any amount to be paid hereunder is stated to be due on a day that
is not a Business Day, such amount shall be payable on the next succeeding
Business Day, and if such payment is timely made, no interest shall accrue for
the period from and after the day on which such payment was due. Interest
payments for this Bond will be computed and paid on the basis of a 360-day year
consisting of twelve 30-day months.


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<PAGE>

      Reference is made to the further provisions of this Bond set forth on the
reverse hereof, which further provisions shall for all purposes have the same
effect as if set forth at this place.

      Unless the certificate of authentication hereon has been executed by the
Trustee by manual signature, this Bond shall not be entitled to any benefit
under the Indenture, or be valid or obligatory for any purpose.

      IN WITNESS WHEREOF, the Issuer has caused this instrument to be duly
executed.

                                        ELWOOD ENERGY LLC


                                        By:
                                           -------------------------------------
                                           Name:
                                           Title:


                                       3
<PAGE>

                          CERTIFICATE OF AUTHENTICATION

Dated:

      This Bond is one of the 8.159% Senior Secured Bonds due July 5, 2026 of
Elwood Energy LLC referred to in the within-mentioned Indenture.

BANK ONE TRUST COMPANY, NATIONAL ASSOCIATION
as Trustee


By:
   ----------------------------------------
      Authorized Signatory

Dated:
      -------------------------------------


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<PAGE>

                               [Form of reverse of
                      8.159% Senior Secured Bonds due 2026]

                                ELWOOD ENERGY LLC
                      8.159% SENIOR SECURED BONDS DUE 2026

      This bond is one of an authorized issue of Bonds of the Issuer known as
its 8.159% Senior Secured Bonds due 2026 (the "Bonds"). The Bonds are issued
under the Trust Indenture dated as of October 23, 2001 (the "Original
Indenture") between the Issuer and Bank One Trust Company, National Association,
a national banking association formed under the laws of the United States, as
trustee (in such capacity, together with its successors in such capacity, the
"Trustee"), as supplemented by the First Supplemental Indenture dated as of
October 23, 2001 (the "First Supplemental Indenture") and the Second
Supplemental Indenture dated as of [______________] (the "Second Supplemental
Indenture") between the Issuer and the Trustee (the Original Indenture, as so
supplemented, and as the same may be amended, modified and further supplemented,
the "Indenture"). All capitalized terms used herein, unless otherwise defined
herein, shall have the meanings ascribed to them in the Indenture.

      All Bonds of any series issued and Outstanding under the Indenture rank on
a parity with each other Bond of the same series and with all Bonds of each
other series. Reference is hereby made to the Indenture for a description of the
nature and extent of the Bonds and the respective rights, limitations of the
rights, duties and immunities thereunder of the Holders of the Bonds and of the
Trustee and the Issuer in respect of the Bonds and the terms upon which the
Bonds are made and are to be authenticated and delivered.

      Except as otherwise specifically provided in the Indenture, the
Intercreditor Agreement or the Deposit and Disbursement Agreement, all payments
of principal of, premium, if any, and interest on this Bond are (i) payable only
from the assets of the Issuer and the income and proceeds thereof received by
the Trustee or the Administrative Agent and allocable to the Trustee therefrom
and (ii) secured by assets subject to the Lien of the Indenture, and all
payments of principal, premium, if any, and interest shall be made in accordance
with the terms of the Indenture. Each Holder, by acceptance of this Bond, hereby
acknowledges and agrees that recourse for any such amounts payable shall be
otherwise limited in accordance with Section 2.15 and Section 14.1 of the
Original Indenture.

      The obligations of the Issuer to pay the principal of and interest on the
Bonds when due as herein prescribed are absolute and unconditional and no
provision of this Bond or the Indenture shall alter or impair such obligations.

      The Indenture permits, with certain exceptions, as therein provided, the
amendment thereof and the modification of the rights and obligations of the
Issuer and the rights

5
<PAGE>

of the Holders of the Bonds under
the Indenture at any time by the Issuer without the consent of the Holders or
with the consent of the Holders of not less than a majority in aggregate
principal amount of the Bonds of all series then Outstanding. The Indenture also
contains provisions permitting the Holders of specified percentages in aggregate
principal amount of the Bonds of all series then Outstanding, on behalf of the
Holders of all the Bonds, to waive compliance by the Issuer with certain
provisions of the Indenture and certain past defaults under the Indenture and
their consequences. Any Act (as such term is defined in the Indenture),
including, but not limited to, such a consent, waiver or direction by the Holder
of this Bond shall be conclusive and binding upon the Holder and upon all future
Holders of this Bond and the Holder of every Bond issued upon the transfer
hereof or the exchange herefor or in lieu hereof whether or not notation of such
Act is made upon this Bond.

      As provided in the Indenture, the aggregate principal amount of Bonds
which may be issued, authenticated and delivered thereunder is unlimited. This
Bond is one of the series designated on the face hereof, limited to $402,000,000
in aggregate principal amount as provided in the First Supplemental Indenture.
All payments of principal and interest made with respect to interests in the
Restricted Global Bond for which interests in this Unrestricted Global Bond were
exchanged on or before the date of authentication of this Unrestricted Global
Bond shall be credited against amounts payable hereunder.

      This Bond and all Bonds issued or to be issued in the series created under
the Second Supplemental Indenture are (i) redeemable at the option of the
Issuer, in accordance with the terms of the Indenture and the First Supplemental
Indenture, and the Issuer is required to redeem this Bond upon the occurrence of
certain specified events pursuant to Section 6.3 of the Indenture and Sections
3.9(c), 3.10(a), 3.10(b) and 3.10(c) of the Deposit and Disbursement Agreement,
and (ii) not subject to any sinking fund.

      Notice of any optional redemption of Bonds will be given at least 30 days
but not more than 60 days before the Redemption Date to each Holder at its
address as it appears in the Security Register.

      Bonds (or portions thereof as aforesaid) for the redemption of which
provision is made in accordance with the Indenture shall cease to bear interest
from and after any Redemption Date.

      The Indenture contains provisions for, upon compliance by the Issuer with
certain conditions set forth in the Indenture, the defeasance of (a) the entire
indebtedness of this Bond and (b) certain restrictive covenants and agreements.

      The unpaid portion of the principal amount hereof, together with any
interest accrued and unpaid thereon and all other amounts due hereunder, if any,
may become due and


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<PAGE>

payable upon the occurrence and during the continuance of any Event of Default,
but only as provided in the Indenture.

      The Bonds are issuable only as registered Bonds without coupons in minimum
denominations of $100,000 and any integral multiple of $100 in excess thereof.

      The transfer of Bonds may be registered and Bonds may be exchanged as
provided in the Indenture. The Security Registrar, the Trustee and the Issuer
may require a Holder, among other things, to pay any taxes and fees required by
law or permitted by the Indenture and to furnish appropriate endorsements and
transfer documents.

      The person in whose name this Bond is registered shall be deemed to be the
owner and holder hereof for the purpose of receiving payment as herein provided
and for all other purposes whether or not this Bond be overdue regardless of any
notice to anyone to the contrary.

      Bonds known to a Responsible Officer of the Trustee to be owned or held
by, or for the account or benefit of, the Issuer or any of the Issuer's members,
or an Affiliate of any of the foregoing, shall not be entitled to share in any
payment or distribution provided for in Article VIII of the Indenture until all
Bonds held by other Persons have been indefeasibly paid in full.

      THIS BOND SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS
OF THE STATE OF NEW YORK.


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<PAGE>

                                  ABBREVIATIONS

      The following abbreviations when used in the inscription on the face of
this instrument shall be construed as though they were written out in full
according to applicable laws or regulations:

                  TEN COM  -   as tenants in common
                  TEN ENT  -   as tenants by the entireties
                  JT TEN   -   as joint tenants with right of survivorship
                               and not as tenants in common

                                UNIF GIFT MIN ACT
                                                 -------------------------------
                                                 (Cust)         (Minor)

                                      under Uniform Gift to Minors Act

                                      ------------------------------------------
                                                        (State)

                Additional abbreviations may also be used though
                              not in the above list

                                 ---------------


                                       8
<PAGE>

      FOR VALUE RECEIVED the undersigned hereby sell(s), assign(s) and
transfer(s) unto

Identifying Number of Assignee
                              -------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
                  (Please print or typewrite name and address,
                         including zip code of Assignee)

the within Bond and all rights thereunder, hereby irrevocably constituting
and appointing ________________________________________ attorney
to transfer said Bond on the books of the Issuer, with full power of
substitution in the premises.

Dated:
      ---------------------

                                                 -------------------------------
                                                 NAME:

NOTICE:     The signature to this assignment must correspond with the name as
            written upon the first page of the within instrument in every
            particular, without alteration or enlargement or any change
            whatsoever.


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<PAGE>

                                                                      ANNEX A TO
                                             8.159% SENIOR SECURED BOND DUE 2026

      The following table sets forth the date of each semiannual installment of
principal to be paid on this Bond and the applicable percentage of the original
principal amount payable on each such date:

                  Scheduled                              Percentage of
                   Payment                                 Principal
                     Date                               Amount Payable
             ---------------------                 ------------------------

                  Jan 5, 2002 ............................. 1.393%
                  Jul 5, 2002 ............................. 0.632
                  Jan 5, 2003 ............................. 2.903
                  Jul 5, 2003 ............................. 0.530
                  Jan 5, 2004 ............................. 2.998
                  Jul 5, 2004 ............................. 0.669
                  Jan 5, 2005 ............................. 3.194
                  Jul 5, 2005 ............................. 0.978
                  Jan 5, 2006 ............................. 3.478
                  Jul 5, 2006 ............................. 1.100
                  Jan 5, 2007 ............................. 3.460
                  Jul 5, 2007 ............................. 1.179
                  Jan 5, 2008 ............................. 3.644
                  Jul 5, 2008 ............................. 1.361
                  Jan 5, 2009 ............................. 3.801
                  Jul 5, 2009 ............................. 1.542
                  Jan 5, 2010 ............................. 4.007
                  Jul 5, 2010 ............................. 1.639
                  Jan 5, 2011 ............................. 4.139
                  Jul 5, 2011 ............................. 1.833
                  Jan 5, 2012 ............................. 4.443
                  Jul 5, 2012 ............................. 2.313
                  Jan 5, 2013 ............................. 5.061
                  Jul 5, 2013 ............................. 0.093
                  Jan 5, 2014 ............................. 1.949
                  Jul 5, 2014 ............................. 0.014
                  Jan 5, 2015 ............................. 1.852
                  Jul 5, 2015 ............................. 0.018
                  Jan 5, 2016 ............................. 2.057


                                       10
<PAGE>

                  Jul 5, 2016 ............................. 0.013%
                  Jan 5, 2017 ............................. 1.421
                  Jul 5, 2017 ............................. 0.064
                  Jan 5, 2018 ............................. 3.212
                  Jul 5, 2018 ............................. 0.081
                  Jan 5, 2019 ............................. 3.592
                  Jul 5, 2019 ............................. 0.042
                  Jan 5, 2020 ............................. 3.846
                  Jul 5, 2020 ............................. 0.265
                  Jan 5, 2021 ............................. 4.879
                  Jul 5, 2021 ............................. 0.130
                  Jan 5, 2022 ............................. 6.410
                  Jul 5, 2022 ............................. 0.401
                  Jan 5, 2023 ............................. 4.991
                  Jul 5, 2023 ............................. 0.161
                  Jan 5, 2024 ............................. 2.366
                  Jul 5, 2024 ............................. 0.192
                  Jan 5, 2025 ............................. 2.991
                  Jul 5, 2025 ............................. 0.291
                  Jan 5, 2026 ............................. 1.943
                  Jul 5, 2026 ............................. 0.429


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<PAGE>

              SCHEDULE OF EXCHANGES OF INTERESTS IN THE GLOBAL BOND

      The following exchanges of a part of this Global Bond for an interest in
another Global Bond or for a Definitive Bond, or exchanges of a part of another
Global Bond or Definitive Bond for an interest in this Global Bond, have been
made:

<Table>
  Date of     Amount of decrease in   Amount of increase in      Principal Amount of          Signature of
 Exchange        Principal Amount       Principal Amount           this Global Bond       authorized officer of
                        of                     of              following such decrease       Trustee or Bond
               this Global Bond        this Global Bond              (or increase)              Custodian
----------   ---------------------    ---------------------    -----------------------    ---------------------
<S>                 <C>                     <C>                      <C>                        <C>

</Table>


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