<PAGE>

                                                                     EXHIBIT 4.3

                TRUST PREFERRED SECURITIES GUARANTEE AGREEMENT


                              AGL Resources Inc.


                           Dated as of May ___, 2001
<PAGE>

                               TABLE OF CONTENTS
                                  (continued)

<TABLE>
<CAPTION>
                                                                                                Page
<S>                                                                                             <C>
                                           ARTICLE I
                                 DEFINITIONS AND INTERPRETATION

SECTION 1.1      Definitions and Interpretation..............................................     1

                                           ARTICLE II
                                      TRUST INDENTURE ACT

SECTION 2.1      Trust Indenture Act; Application............................................     5

SECTION 2.2      Lists of Holders of Securities..............................................     5

SECTION 2.3      Reports by the Guarantee Trustee............................................     5

SECTION 2.4      Periodic Reports to Guarantee Trustee.......................................     5

SECTION 2.5      Evidence of Compliance with Conditions Precedent............................     6

SECTION 2.6      Events of Default; Waiver...................................................     6

SECTION 2.7      Event of Default; Notice....................................................     6

SECTION 2.8      Conflicting Interests.......................................................     7

                                           ARTICLE III
                          POWERS, DUTIES AND RIGHTS OF GUARANTEE TRUSTEE

SECTION 3.1      Powers and Duties of the Guarantee Trustee..................................     7

SECTION 3.2      Certain Rights of Guarantee Trustee.........................................     8

SECTION 3.3      Not Responsible for Recitals or Issuance of Guarantee.......................    10

                                           ARTICLE IV
                                       GUARANTEE TRUSTEE

SECTION 4.1      Guarantee Trustee; Eligibility..............................................    11

SECTION 4.2      Appointment, Removal and Resignation of Guarantee Trustee...................    11

                                           ARTICLE V
                                           GUARANTEE

SECTION 5.1      Guarantee...................................................................    12

SECTION 5.2      Waiver of Notice and Demand.................................................    12

SECTION 5.3      Obligations Not Affected....................................................    12

SECTION 5.4      Rights of Holders...........................................................    13

SECTION 5.5      Guarantee of Payment........................................................    14

SECTION 5.6      Subrogation.................................................................    14

SECTION 5.7      Independent Obligations.....................................................    14
</TABLE>

                                      -i-
<PAGE>

                               TABLE OF CONTENTS
                                  (continued)


<TABLE>
<CAPTION>
                                                                                                Page
<S>                                                                                             <C>
                                           ARTICLE VI
                            LIMITATION OF TRANSACTIONS; SUBORDINATION

SECTION 6.1      Limitation of Transactions..................................................    14

SECTION 6.2      Ranking.....................................................................    15

                                           ARTICLE VII
                                           TERMINATION

SECTION 7.1      Termination.................................................................    15

                                           ARTICLE VIII
                           COMPENSATION AND EXPENSES OF GUARANTEE TRUSTEE

                                            ARTICLE IX
                                         INDEMNIFICATION

SECTION 9.1      Exculpation.................................................................    16

SECTION 9.2      Indemnification.............................................................    16

                                            ARTICLE X
                                          MISCELLANEOUS

SECTION 10.1     Successors and Assigns......................................................    17

SECTION 10.2     Amendments..................................................................    17

SECTION 10.3     Notices.....................................................................    17

SECTION 10.4     Benefit.....................................................................    18

SECTION 10.5     Governing Law...............................................................    18
</TABLE>

                                      -ii-
<PAGE>

                TRUST PREFERRED SECURITIES GUARANTEE AGREEMENT

          This Trust Preferred Securities Guarantee Agreement (the "Guarantee"),
dated as of May ___, 2001, is executed and delivered by AGL Resources Inc., a
Georgia corporation (the "Guarantor"), and The Bank of New York, a New York
banking corporation, as trustee (the "Guarantee Trustee"), for the benefit of
the Holders (as defined herein) from time to time of the Trust Preferred
Securities (as defined herein) of AGL Capital Trust II, a Delaware statutory
business trust (the "Trust").

          WHEREAS, pursuant to an Amended and Restated Trust Agreement (the
"Trust Agreement"), dated as of May ___, 2001, among the trustees of the Trust,
AGL Capital Corporation, as sponsor, and the holders from time to time of
undivided beneficial interests in the assets of the Trust, the Trust is issuing
on the date hereof  preferred securities, having an aggregate liquidation amount
of $150,000,000, such Trust Preferred Securities being designated the _____%
Trust Preferred Securities (the "Trust Preferred Securities").

          WHEREAS, as incentive for the Holders to purchase the Trust Preferred
Securities, the Guarantor desires irrevocably and unconditionally to agree, to
the extent set forth in this Guarantee, to pay to the Holders the Guarantee
Payments (as defined below).  The Guarantor agrees to make certain other
payments on the terms and conditions set forth herein.

          NOW, THEREFORE, in consideration of the purchase by each Holder, which
purchase the Guarantor hereby acknowledges shall benefit the Guarantor, the
Guarantor executes and delivers this Guarantee for the benefit of the Holders.

                                   ARTICLE I
                        DEFINITIONS AND INTERPRETATION

SECTION 1.1  Definitions and Interpretation
             ------------------------------

          In this Guarantee, unless the context otherwise requires:

          (a)  Capitalized terms used in this Guarantee but not defined in the
               preamble above have the respective meanings assigned to them in
               this Section 1.1;

          (b)  Terms defined in the Trust Agreement as of the date of execution
               of this Guarantee have the same meaning when used in this
               Guarantee;

          (c)  a term defined anywhere in this Guarantee has the same meaning
               throughout;

                                       1
<PAGE>

          (d)  all references to "the Guarantee" or "this Guarantee" are to this
               Trust Preferred Securities Guarantee as modified, supplemented or
               amended from time to time;

          (e)  all references in this Guarantee to Articles and Sections are to
               Articles and Sections of this Guarantee, unless otherwise
               specified;

          (f)  a term defined in the Trust Indenture Act has the same meaning
               when used in this Guarantee, unless otherwise defined in this
               Guarantee or unless the context otherwise requires; and

          (g)  a reference to the singular includes the plural and vice versa.

          "Affiliate" has the same meaning as given to that term in Rule 405
           ---------
under the Securities Act of 1933, as amended, or any successor rule thereunder.

          "Business Day" means any day other than a Saturday or a Sunday, or a
           ------------
day on which banking institutions in The City of New York are authorized or
required by law or executive order to close.

          "Common Securities" means the securities representing common undivided
           -----------------
beneficial interests in the assets of the Trust.

          "Corporate Trust Office" means the office of the Guarantee Trustee at
           ----------------------
which the corporate trust business of the Guarantee Trustee shall, at any
particular time, be principally administered, which office at the date of
execution of this Guarantee is located at 101 Barclay Street, 21 West, New York,
New York  10286.

          "Covered Person" means any Holder or beneficial owner of Trust
           --------------
Preferred Securities.

          "Debentures" means the series of subordinated debt securities of AGL
           ----------
Capital Corporation designated the ______% Junior Subordinated Deferrable
Interest Debentures due _________ 1, 2041 held by the Property Trustee of the
Trust.

          "Event of Default" means a default by the Guarantor on any of its
           ----------------
payment or other obligations under this Guarantee.

          "Guarantee Payments" means the following payments or distributions,
           ------------------
without duplication, with respect to the Trust Preferred Securities, to the
extent not paid or made by the Trust:  (i) any accumulated and unpaid
Distributions (as defined in the Trust Agreement) that are required to be paid
on such Trust Preferred Securities to the extent the Trust has funds on hand
legally available therefor at such time, (ii) the redemption price, including
all accumulated and unpaid Distributions to the date of redemption (the
"Redemption Price") to the extent the Trust has funds on hand legally available
therefor at such time, with respect to any Trust Preferred

                                       2
<PAGE>

Securities called for redemption by the Trust, and (iii) upon a voluntary or
involuntary termination and liquidation of the Trust (other than in connection
with the distribution of Debentures to the Holders in exchange for Trust
Preferred Securities as provided in the Trust Agreement), the lesser of (a) the
aggregate of the liquidation amount and all accumulated and unpaid Distributions
on the Trust Preferred Securities to the date of payment, to the extent the
Trust has funds on hand legally available therefor, and (b) the amount of assets
of the Trust remaining available for distribution to Holders in liquidation of
the Trust.

          "Guarantee Trustee" means The Bank of New York, a New York banking
           -----------------
corporation, until a Successor Guarantee Trustee has been appointed and has
accepted such appointment pursuant to the terms of this Guarantee and thereafter
means each such Successor Guarantee Trustee.

          "Holder" shall mean any holder, as registered on the books and records
           ------
of the Trust, of any Trust Preferred Securities; provided, however, that, in
determining whether the holders of the requisite percentage of Trust Preferred
Securities have given any request, notice, consent or waiver hereunder, "Holder"
shall not include the Guarantor or any Affiliate of the Guarantor.

          "Indemnified Person" means the Guarantee Trustee, any Affiliate of the
           ------------------
Guarantee Trustee, or any officers, directors, shareholders, members, partners,
employees, representatives, nominees, custodians or agents of the Guarantee
Trustee.

          "Indenture" means the Indenture dated as of May ___, 2001, among AGL
           ---------
Resources Inc., AGL Capital Corporation (the "Debenture Issuer") and The Bank of
New York, as trustee (the "Property Trustee"), pursuant to which the Debentures
are to be issued to the Property Trustee of the Trust.

          "Indenture Event of Default" shall mean any event specified in Section
           --------------------------
5.01 of the Indenture.

          "Majority in liquidation amount of the Trust Preferred Securities"
           ----------------------------------------------------------------
means, except as provided by the Trust Indenture Act, a vote by Holder(s) of
more than 50% of the aggregate liquidation amount (including the stated amount
that would be paid on redemption, liquidation or otherwise, plus accumulated and
unpaid Distributions to the date upon which the voting percentages are
determined) of all Trust Preferred Securities.

          "Officer's Certificate" means, with respect to any person, a
           ---------------------
certificate signed by the Chairman, the Chief Executive Officer, the President,
a Vice President, the Controller, the Secretary or an Assistant Secretary, the
Treasurer or an Assistant Treasurer of the Guarantor.  Any Officers' Certificate
delivered with respect to compliance with a condition or covenant provided for
in this Guarantee shall include:

          (a)  a statement that each officer signing the Officers' Certificate
     has read the covenant or condition and the definitions relating thereto;

                                       3
<PAGE>

          (b)  a statement that each such officer has made such examination or
     investigation as, in such officer's opinion, is necessary to enable such
     officer to express an informed opinion as to whether or not such covenant
     or condition has been complied with; and

          (c)  a statement as to whether, in the opinion of each such officer,
     such condition or covenant has been complied with.

          "Other Debentures" means all junior subordinated debentures issued by
           ----------------
the Guarantor or the Company from time to time and sold to trusts to be
established by the Guarantor or the Company (if any), in each case similar to
the Trust.

          "Other Guarantees" means all guarantees to be issued by the Guarantor
           ----------------
with respect to Trust Preferred Securities (if any) similar to the Trust
Preferred Securities issued by other trusts to be established by the Guarantor
or the Company (if any), in each case similar to the Trust.

          "Person" means a legal person, including any individual, corporation,
           ------
estate, partnership, joint venture, association, joint stock company, limited
liability company, trust, unincorporated association, or government or any
agency or political subdivision thereof, or any other entity of whatever nature.

          "Redemption Price" has the meaning provided therefor in the definition
           ----------------
of Guarantee Payments.

          "Responsible Officer" shall mean, when used with respect to the
           -------------------
Guarantee Trustee, any officer within the corporate trust office of the
Guarantee Trustee, including any vice-president, any assistant vice-president,
assistant secretary, assistant treasurer, trust officer or any other officer of
the Guarantee Trustee who customarily performs functions similar to those
performed by the Person who at the time shall be such officer, respectively, or
to whom any corporate trust matter is referred because of such person's
knowledge of and familiarity with the particular subject and who shall have
direct responsibility for the administration of the Trust.

          "Successor Guarantee Trustee" means a successor Guarantee Trustee
           ---------------------------
possessing the qualifications to act as Guarantee Trustee under Section 4.1.

          "Trust Indenture Act" means the Trust Indenture Act of 1939, as
           -------------------
amended.

          "Trust Securities" means the Common Securities and the Trust Preferred
           ----------------
Securities, collectively.

                                       4
<PAGE>

                                  ARTICLE II
                              TRUST INDENTURE ACT

SECTION 2.1   Trust Indenture Act; Application
              --------------------------------

              (a)  This Guarantee is subject to the provisions of the Trust
Indenture Act that are required to be part of this Guarantee and shall, to the
extent applicable, be governed by such provisions; and

              (b)  if and to the extent that any provision of this Guarantee
limits, qualifies or conflicts with the duties imposed by Section 310 to 317,
inclusive, of the Trust Indenture Act, such imposed duties shall control.

SECTION 2.2   Lists of Holders of Securities
              ------------------------------

              (a)  The Guarantor shall provide the Guarantee Trustee (unless the
Guarantee Trustee is otherwise the registrar of the Trust Preferred Securities)
with a list, in such form as the Guarantee Trustee may reasonably require, of
the names and addresses of the Holders ("List of Holders") as of such date, (i)
not more than 15 days after each record date for payment of Distributions, and
(ii) at any other time within 30 days of receipt by the Guarantor of a written
request for a List of Holders as of a date not more than 15 days before such
List of Holders is given to the Guarantee Trustee provided, that the Guarantor
                                                  --------
shall not be obligated to provide such List of Holders at any time the List of
Holders does not differ from the most recent List of Holders given to the
Guarantee Trustee by the Guarantor. The Guarantee Trustee may destroy any List
of Holders previously given to it on receipt of a new List of Holders.

              (b)  The Guarantee Trustee shall comply with its obligations under
Sections 311(a), 311(b) and Section 312(b) of the Trust Indenture Act.

SECTION 2.3   Reports by the Guarantee Trustee
              --------------------------------

              Within 60 days after July 15 of each year, commencing July 15,
2002, the Guarantee Trustee shall provide to the Holders such reports as are
required by Section 313(a) of the Trust Indenture Act, if any, in the form and
in the manner provided by Section 313 of the Trust Indenture Act. The Guarantee
Trustee shall also comply with the other requirements of Section 313 of the
Trust Indenture Act.

SECTION 2.4   Periodic Reports to Guarantee Trustee
              -------------------------------------

              The Guarantor shall provide to the Guarantee Trustee such
documents, reports and information as required by Section 314 (if any) and the
compliance certificate required by Section 314 of the Trust Indenture Act in the
form, in the manner and at the times required by Section 314 of the Trust
Indenture Act provided that such compliance certificate shall be delivered on or
before 120 days after the end of each fiscal year of the Guarantor. Delivery of
such reports, information and documents to the Guarantee Trustee is for
informational purposes

                                       5
<PAGE>

only and the Guarantee Trustee's receipt of such shall not constitute
constructive notice of any information contained therein or determinable from
information contained therein, including the Guarantor's compliance with any of
its covenants hereunder (as to which the Guarantee Trustee is entitled to rely
exclusively on Officers' Certificates).

             Delivery of such reports, information and documents to the Trustee
is for informational purposes only and the Trustee's receipt of such shall not
constitute constructive notice of any information contained therein or
determinable from information contained therein, including the Trust's
compliance with any of its covenants hereunder (as to which the Trustee is
entitled to rely exclusively on Officer's Certificates).

SECTION 2.5  Evidence of Compliance with Conditions Precedent
             ------------------------------------------------

             The Guarantor shall provide to the Guarantee Trustee such evidence
of compliance with any conditions precedent, if any, provided for in this
Guarantee that relate to any of the matters set forth in Section 314(c) of the
Trust Indenture Act. Any certificate or opinion required to be given by an
officer pursuant to Section 314(c)(1) may be given in the form of an Officers'
Certificate.

SECTION 2.6  Events of Default; Waiver
             -------------------------

             The Holders of a Majority in liquidation amount of Trust Preferred
Securities may, by vote, on behalf of all the Holders, waive any past Event of
Default and its consequences.  Upon such waiver, any such Event of Default shall
cease to exist, and any Event of Default arising therefrom shall be deemed to
have been cured, for every purpose of this Guarantee, but no such waiver shall
extend to any subsequent or other default or Event of Default or impair any
right consequent thereon.

SECTION 2.7  Event of Default; Notice
             ------------------------

             (a)  The Guarantee Trustee shall, within 90 days after the
occurrence of a default with respect to this Guarantee, mail by first class
postage prepaid, to all Holders, notices of all defaults actually known to a
Responsible Officer of the Guarantee Trustee, unless such defaults have been
cured before the giving of such notice, provided, that, except in the case of
default in the payment of any Guarantee Payment, the Guarantee Trustee shall be
protected in withholding such notice if and so long as the board of directors,
the executive committee, or a trust committee of directors and/or Responsible
Officers of the Guarantee Trustee in good faith determines that the withholding
of such notice is in the interests of the holders of the Trust Preferred
Securities.

             (b)  The Guarantee Trustee shall not be deemed to have knowledge of
any Event of Default unless the Guarantee Trustee shall have received written
notice from the Guarantor or a Holder, or a Responsible Officer of the Guarantee
Trustee charged with the administration of the Trust Agreement shall have
obtained actual knowledge, of such Event of Default.

                                       6
<PAGE>

SECTION 2.8  Conflicting Interests
             ---------------------

             The Trust Agreement shall be deemed to be specifically described in
this Guarantee for the purposes of clause (i) of the first proviso contained in
Section 310(b) of the Trust Indenture Act.

                                  ARTICLE III
                POWERS, DUTIES AND RIGHTS OF GUARANTEE TRUSTEE

SECTION 3.1  Powers and Duties of the Guarantee Trustee
             ------------------------------------------

             (a)  This Guarantee shall be held by the Guarantee Trustee for the
benefit of the Holders, and the Guarantee Trustee shall not transfer this
Guarantee to any Person except a Holder exercising his or her rights pursuant to
Section 5.4(b) or to a Successor Guarantee Trustee on acceptance by such
Successor Guarantee Trustee of its appointment to act as Successor Guarantee
Trustee. The right, title and interest of the Guarantee Trustee shall
automatically vest in any Successor Guarantee Trustee, and such vesting and
succession of title shall be effective whether or not conveyancing documents
have been executed and delivered pursuant to the appointment of such Successor
Guarantee Trustee.

             (b)  If an Event of Default actually known to a Responsible Officer
of the Guarantee Trustee has occurred and is continuing, the Guarantee Trustee
shall enforce this Guarantee for the benefit of the Holders.

             (c)  The Guarantee Trustee, before the occurrence of any Event of
Default and after the curing of all Events of Default that may have occurred,
shall undertake to perform only such duties as are specifically set forth in
this Guarantee, and no implied covenants shall be read into this Guarantee
against the Guarantee Trustee. In case an Event of Default has occurred (that
has not been cured or waived pursuant to Section 2.6) and is actually known to a
Responsible Officer of the Guarantee Trustee, the Guarantee Trustee shall
exercise such of the rights and powers vested in it by this Guarantee, and use
the same degree of care and skill in its exercise thereof, as a prudent person
would exercise or use under the circumstances in the conduct of his or her own
affairs.

             (d)  No provision of this Guarantee shall be construed to relieve
the Guarantee Trustee from liability for its own negligent action, its own
negligent failure to act, or its own willful misconduct, except that:

             (i)  prior to the occurrence of any Event of Default and after the
     curing or waiving of all such Events of Default that may have occurred:

                  (A)  the duties and obligations of the Guarantee Trustee shall
             be determined solely by the express provisions of this Guarantee,
             and the Guarantee Trustee shall not be liable except for the
             performance of such duties and obligations as are specifically set
             forth in this Guarantee, and no implied

                                       7
<PAGE>

             covenants or obligations shall be read into this Guarantee against
             the Guarantee Trustee; and

                    (B)  in the absence of bad faith on the part of the
             Guarantee Trustee, the Guarantee Trustee may conclusively rely, as
             to the truth of the statements and the correctness of the opinions
             expressed therein, upon any certificates or opinions furnished to
             the Guarantee Trustee and conforming to the requirements of this
             Guarantee; but in the case of any such certificates or opinions
             that by any provision hereof are specifically required to be
             furnished to the Guarantee Trustee, the Guarantee Trustee shall be
             under a duty to examine the same to determine whether or not they
             conform to the requirements of this Guarantee. The Trustee shall
             not be bound to make any investigation into the facts or matters
             stated in any resolution, certificate, statement, instrument,
             opinion, report, notice, request, direction, consent, order, bond,
             debenture, note, other evidence of indebtedness or other paper or
             document, but the Trustee, in its discretion, may make such further
             inquiry or investigation into such facts or matters as it may see
             fit, and, if the Trustee shall determine to make such further
             inquiry or investigation, it shall be entitled to examine the
             books, records and premises of the Guarantor, personally or by
             agent or attorney at the sole cost of the Guarantor and shall incur
             no liability or additional liability of any kind by reason of such
             inquiry or investigation;

             (ii)   the Guarantee Trustee shall not be liable for any error of
     judgment made in good faith by a Responsible Officer of the Guarantee
     Trustee, unless it shall be proved that the Guarantee Trustee was negligent
     in ascertaining the pertinent facts upon which such judgment was made;

             (iii)  the Guarantee Trustee shall not be liable with respect to
     any action taken or omitted to be taken by it in good faith in accordance
     with the direction of the Holders of a Majority in liquidation amount of
     the Trust Preferred Securities relating to the time, method and place of
     conducting any proceeding for any remedy available to the Guarantee
     Trustee, or exercising any trust or power conferred upon the Guarantee
     Trustee under this Guarantee; and

             (iv)   no provision of this Guarantee shall require the Guarantee
     Trustee to expend or risk its own funds or otherwise incur personal
     financial liability in the performance of any of its duties or in the
     exercise of any of its rights or powers, if the Guarantee Trustee shall
     have reasonable grounds for believing that the repayment of such funds or
     liability is not reasonably assured to it under the terms of this Guarantee
     or indemnity, reasonably satisfactory to the Guarantee Trustee, against
     such risk or liability is not reasonably assured to it.

SECTION 3.2  Certain Rights of Guarantee Trustee
             -----------------------------------

             (a)    Subject to the provisions of Section 3.1:

                                       8
<PAGE>

          (i)    The Guarantee Trustee may conclusively rely, and shall be fully
     protected in acting or refraining from acting, upon any resolution,
     certificate, statement, instrument, opinion, report, notice, request,
     direction, consent, order, bond, debenture, note, other evidence of
     indebtedness or other paper or document believed by it to be genuine and to
     have been signed, sent or presented by the proper party or parties.

          (ii)   Any direction or act of the Guarantor contemplated by this
     Guarantee may be sufficiently evidenced by an Officers' Certificate.

          (iii)  Whenever, in the administration of this Guarantee, the
     Guarantee Trustee shall deem it desirable that a matter be proved or
     established before taking, suffering or omitting any action hereunder, the
     Guarantee Trustee (unless other evidence is herein specifically prescribed)
     may, in the absence of bad faith on its part, request and conclusively rely
     upon an Officers' Certificate which, upon receipt of such request, shall be
     promptly delivered by the Guarantor.

          (iv)   The Guarantee Trustee shall have no duty to see to any
     recording, filing or registration of any instrument (or any rerecording,
     refiling or registration thereof).

          (v)    The Guarantee Trustee may consult with counsel of its
     selection, and the advice or opinion of such counsel with respect to legal
     matters shall be full and complete authorization and protection in respect
     of any action taken, suffered or omitted by it hereunder in good faith and
     in accordance with such advice or opinion. Such counsel may be counsel to
     the Guarantor or any of its Affiliates and may include any of its
     employees. The Guarantee Trustee shall have the right at any time to seek
     instructions concerning the administration of this Guarantee from any court
     of competent jurisdiction.

          (vi)   The Guarantee Trustee shall be under no obligation to exercise
     any of the rights or powers vested in it by this Guarantee at the request
     or direction of any Holder, unless such Holder shall have provided to the
     Guarantee Trustee such security and indemnity, reasonably satisfactory to
     the Guarantee Trustee, against the costs, expenses (including attorneys'
     fees and expenses and the expenses of the Guarantee Trustee's agents,
     nominees or custodians) and liabilities that might be incurred by it in
     complying with such request or direction, including such reasonable
     advances as may be requested by the Guarantee Trustee; provided that,
     nothing contained in this Section 3.2(a)(vi) shall be taken to relieve the
     Guarantee Trustee, upon the occurrence of an Event of Default, of its
     obligation to exercise the rights and powers vested in it by this
     Guarantee.

          (vii)  The Guarantee Trustee shall not be bound to make any
     investigation into the facts or matters stated in any resolution,
     certificate, statement, instrument, opinion, report, notice, request,
     direction, consent, order, bond, debenture, note, other evidence of
     indebtedness or other paper or document, but the Guarantee Trustee, in its
     discretion, may make such further inquiry or investigation into such facts
     or matters as it may see fit.

                                       9
<PAGE>

               (viii) The Guarantee Trustee may execute any of the trusts or
     powers hereunder or perform any duties hereunder either directly or by or
     through agents, nominees, custodians or attorneys, and the Guarantee
     Trustee shall not be responsible for any misconduct or negligence on the
     part of any agent or attorney appointed with due care by it hereunder.

               (ix)   Any action taken by the Guarantee Trustee or its agents
     hereunder shall bind the Holders, and the signature of the Guarantee
     Trustee or its agents alone shall be sufficient and effective to perform
     any such action. No third party shall be required to inquire as to the
     authority of the Guarantee Trustee to so act or as to its compliance with
     any of the terms and provisions of this Guarantee, both of which shall be
     conclusively evidenced by the Guarantee Trustee's or its agent's taking
     such action.

               (x)    Whenever in the administration of this Guarantee the
     Guarantee Trustee shall deem it desirable to receive instructions with
     respect to enforcing any remedy or right or taking any other action
     hereunder, the Guarantee Trustee (i) may request instructions from the
     Holders of a Majority in liquidation amount of the Trust Preferred
     Securities, (ii) may refrain from enforcing such remedy or right or taking
     such other action until such instructions are received, and (iii) shall be
     protected in conclusively relying on or acting in accordance with such
     instructions.

               (xi)   The Guarantee Trustee shall not be liable for any action
     taken, suffered, or omitted to be taken by it in good faith, without
     negligence, and reasonably believed by it to be authorized or within the
     discretion or rights or powers conferred upon it by this Guarantee.

               (b)    No provision of this Guarantee shall be deemed to impose
any duty or obligation on the Guarantee Trustee to perform any act or acts or
exercise any right, power, duty or obligation conferred or imposed on it in any
jurisdiction in which it shall be illegal, or in which the Guarantee Trustee
shall be unqualified or incompetent in accordance with applicable law, to
perform any such act or acts or to exercise any such right, power, duty or
obligation. No permissive power or authority available to the Guarantee Trustee
shall be construed to be a duty.

               (c)    Whether or not therein expressly so provided, every
provision of this Guarantee relating to the conduct or affecting the liability
of or affording protection to the Guarantee Trustee shall be subject to the
provisions of this Section.

SECTION 3.3    Not Responsible for Recitals or Issuance of Guarantee
               -----------------------------------------------------

               The recitals contained in this Guarantee shall be taken as the
statements of the Guarantor, and the Guarantee Trustee does not assume any
responsibility for their correctness.  The Guarantee Trustee makes no
representation as to the validity or sufficiency of this Guarantee.

                                       10
<PAGE>

                                  ARTICLE IV
                               GUARANTEE TRUSTEE

SECTION 4.1    Guarantee Trustee; Eligibility
               ------------------------------

               (a)  There shall at all times be a Guarantee Trustee which shall:

               (i)  not be an Affiliate of the Guarantor; and

               (ii) be a corporation organized and doing business under the laws
     of the United States of America or any State or Territory thereof or of the
     District of Columbia, or a corporation or Person permitted by the
     Securities and Exchange Commission to act as an institutional trustee under
     the Trust Indenture Act, authorized under such laws to exercise corporate
     trust powers, having a combined capital and surplus of at least 50 million
     U.S. dollars ($50,000,000), and subject to supervision or examination by
     Federal, State, Territorial or District of Columbia authority. If such
     corporation publishes reports of condition at least annually, pursuant to
     law or to the requirements of the supervising or examining authority
     referred to above, then, for the purposes of this Section 4.1(a)(ii), the
     combined capital and surplus of such corporation shall be deemed to be its
     combined capital and surplus as set forth in its most recent report of
     condition so published.

               (b)  If at any time the Guarantee Trustee shall cease to be
eligible to so act under Section 4.1(a), the Guarantee Trustee shall immediately
resign in the manner and with the effect set out in Section 4.2(c).

               (c)  If the Guarantee Trustee has or shall acquire any
"conflicting interest" within the meaning of Section 310(b) of the Trust
Indenture Act, the Guarantee Trustee and Guarantor shall in all respects comply
with the provisions of Section 310(b) of the Trust Indenture Act, subject to the
penultimate paragraph thereof.

SECTION 4.2    Appointment, Removal and Resignation of Guarantee Trustee
               ---------------------------------------------------------

               (a)  Subject to Section 4.2(b), the Guarantee Trustee may be
appointed or removed without cause at any time by the Guarantor except during an
Event of Default.

               (b)  The Guarantee Trustee shall not be removed in accordance
with Section 4.2(a) until a Successor Guarantee Trustee has been appointed and
has accepted such appointment by written instrument executed by such Successor
Guarantee Trustee and delivered to the Guarantor.

               (c)  The Guarantee Trustee shall hold office until a Successor
Guarantee Trustee shall have been appointed or until its removal or resignation.
The Guarantee Trustee may resign from office (without need for prior or
subsequent accounting) by an instrument in writing executed by the Guarantee
Trustee and delivered to the Guarantor, which resignation shall not take effect
until a Successor Guarantee Trustee has been appointed and has accepted

                                       11
<PAGE>

such appointment by instrument in writing executed by such Successor Guarantee
Trustee and delivered to the Guarantor and the resigning Guarantee Trustee.

               (d)  If no Successor Guarantee Trustee shall have been appointed
and accepted appointment as provided in this Section 4.2 within 60 days after
delivery of an instrument of removal or resignation, the Guarantee Trustee
resigning or being removed may petition any court of competent jurisdiction for
appointment of a Successor Guarantee Trustee. Such court may thereupon, after
prescribing such notice, if any, as it may deem proper, appoint a Successor
Guarantee Trustee.

               (e)  No Guarantee Trustee shall be liable for the acts or
omissions to act of any Successor Guarantee Trustee.

               (f)  Upon termination of this Guarantee or removal or resignation
of the Guarantee Trustee pursuant to this Section 4.2, the Guarantor shall pay
to the Guarantee Trustee all amounts due to the Guarantee Trustee accrued to the
date of such termination, removal or resignation.

                                   ARTICLE V
                                   GUARANTEE

SECTION 5.1    Guarantee
               ---------

               The Guarantor irrevocably and unconditionally agrees to pay in
full to the Holders the Guarantee Payments (without duplication of amounts
theretofore paid by the Trust), as and when due, regardless of any defense,
right of set-off or counterclaim that the Trust may have or assert. The
Guarantor's obligation to make a Guarantee Payment may be satisfied by direct
payment of the required amounts by the Guarantor to the Holders or by causing
the Trust to pay such amounts to the Holders.

SECTION 5.2    Waiver of Notice and Demand
               ---------------------------

               The Guarantor hereby waives notice of acceptance of this
Guarantee and of any liability to which it applies or may apply, presentment,
demand for payment, any right to require a proceeding first against the Trust or
any other Person before proceeding against the Guarantor, protest, notice of
nonpayment, notice of dishonor, notice of redemption and all other notices and
demands.

SECTION 5.3    Obligations Not Affected
               ------------------------

               The obligations, covenants, agreements and duties of the
Guarantor under this Guarantee shall in no way be affected or impaired by reason
of the happening from time to time of any of the following:

                                       12
<PAGE>

               (a)  the release or waiver, by operation of law or otherwise, of
the performance or observance by the Trust of any express or implied agreement,
covenant, term or condition relating to the Trust Preferred Securities to be
performed or observed by the Trust;

               (b)  the extension of time for the payment by the Trust of all or
any portion of the Distributions, Redemption Price, Liquidation Distribution or
any other sums payable under the terms of the Trust Preferred Securities or the
extension of time for the performance of any other obligation under, arising out
of, or in connection with, the Trust Preferred Securities (other than an
extension of time for payment of Distributions, Redemption Price, Liquidation
Distribution or other sum payable that results from the extension of any
interest payment period on the Debentures permitted by the Indenture);

               (c)  any failure, omission, delay or lack of diligence on the
part of the Holders to enforce, assert or exercise any right, privilege, power
or remedy conferred on the Holders pursuant to the terms of the Trust Preferred
Securities, or any action on the part of the Trust granting indulgence or
extension of any kind;

               (d)  the voluntary or involuntary liquidation, dissolution, sale
of any collateral, receivership, insolvency, bankruptcy, assignment for the
benefit of creditors, reorganization, arrangement, composition or readjustment
of debt of, or other similar proceedings affecting, the Trust or any of the
assets of the Trust;

               (e)  any invalidity of, or defect or deficiency in, the Trust
Preferred Securities;

               (f)  the settlement or compromise of any obligation guaranteed
hereby or hereby incurred; or

               (g)  any other circumstance whatsoever that might otherwise
constitute a legal or equitable discharge or defense of a guarantor, it being
the intent of this Section 5.3 that the obligations of the Guarantor with
respect to the Guarantee Payments shall be absolute and unconditional under any
and all circumstances.

               There shall be no obligation of the Holders to give notice to, or
obtain consent of, the Guarantor with respect to the happening of any of the
foregoing.

SECTION 5.4    Rights of Holders
               -----------------

               (a)  The Holders of a Majority in liquidation amount of the Trust
Preferred Securities have the right to direct the time, method and place of
conducting any proceeding for any remedy available to the Guarantee Trustee in
respect of this Guarantee or exercising any trust or power conferred upon the
Guarantee Trustee under this Guarantee.

               (b)  Any Holder may institute a legal proceeding directly against
the Guarantor to enforce the Guarantee Trustee's rights under this Guarantee,
without first instituting a legal proceeding against the Trust, the Guarantee
Trustee or any other person or entity.

                                       13
<PAGE>

SECTION 5.5    Guarantee of Payment
               --------------------

               This Guarantee creates a guarantee of payment and not of
collection.

SECTION 5.6    Subrogation
               -----------

               The Guarantor shall be subrogated to all (if any) rights of the
Holders against the Trust in respect of any amounts paid to such Holders by the
Guarantor under this Guarantee; provided, however, that the Guarantor shall not
(except to the extent required by mandatory provisions of law) be entitled to
enforce or exercise any right that it may acquire by way of subrogation or any
indemnity, reimbursement or other agreement, in all cases as a result of payment
under this Guarantee, if, at the time of any such payment, any amounts are due
and unpaid under this Guarantee.  If any amount shall be paid to the Guarantor
in violation of the preceding sentence, the Guarantor agrees to hold such amount
in trust for the Holders and to pay over such amount to the Holders.

SECTION 5.7    Independent Obligations
               -----------------------

               The Guarantor acknowledges that its obligations hereunder are
independent of the obligations of the Trust with respect to the Trust Preferred
Securities, and that the Guarantor shall be liable as principal and as debtor
hereunder to make Guarantee Payments pursuant to the terms of this Guarantee
notwithstanding the occurrence of any event referred to in subsections (a)
through (h), inclusive, of Section 5.3 hereof.

                                  ARTICLE VI
                   LIMITATION OF TRANSACTIONS; SUBORDINATION

SECTION 6.1    Limitation of Transactions
               --------------------------

               So long as any Trust Preferred Securities remain outstanding, the
Guarantor shall not (i) declare or pay any dividends or distributions on, or
redeem, purchase, acquire or make a liquidation payment with respect to, any of
the Guarantor's capital stock (which includes common and preferred stock) or
(ii) make any payment of principal of or premium, if any, or interest on or
repay, repurchase or redeem any debt securities of the Guarantor (including
Other Debentures) that rank pari passu with or junior in right of payment to the
Debentures or (iii) make any guarantee payments with respect to any guarantee by
the Guarantor of the debt securities of any subsidiary of the Guarantor
(including Other Guarantees) if such guarantee ranks pari passu with or junior
in right of payment to the Debentures (other than (a) dividends or distributions
in shares of, or options, warrants, rights to subscribe for or purchase shares
of, common stock of the Guarantor, (b) any declaration of a dividend in
connection with the implementation of a stockholders' rights plan, or the
issuance of stock under any such plan in the future, or the redemption or
repurchase of any such rights pursuant thereto, (c) payments under the
Guarantee, (d) the purchase of fractional shares resulting from a
reclassification of the Guarantor's capital stock, (e) the exchange or the
conversion of one class, or series of the Guarantor's capital stock for another
class or series of the Guarantor's capital stock, and (f) the

                                       14
<PAGE>

purchase of fractional interests in shares of the Guarantor's capital stock
pursuant to the conversion or exchange provisions of such capital stock or the
security being converted or exchanged) if at such time (1) there shall have
occurred and be continuing an event of default under the Trust Agreement, (2)
there shall have occurred and be continuing an Event of Default under the
Indenture, (3) there shall have occurred and be continuing a payment default
under the Trust Agreement or the Indenture, (4) if the Debentures are held by
the Trust, the Guarantor shall be in default with respect to its payment of any
obligations under this Guarantee, or (5) the Guarantor shall have given notice
of its election of an Extended Interest Payment Period (as defined in the
Indenture) and shall not have rescinded such notice, and such Extended Interest
Payment Period, or any extension thereof, shall have commenced.

SECTION 6.2    Ranking
               -------

               This Guarantee will constitute an unsecured obligation of the
Guarantor and will rank (i) subordinate and junior in right of payment to Senior
Indebtedness (as defined in the Indenture assuming the Guarantor is an "obligor"
as described therein, the term "Securities" means the Guarantee and the term
"Company" means the Guarantor), to the same extent and in the same manner that
the Debentures are subordinated to Senior Indebtedness pursuant to the
Indenture, it being understood that the terms of Article XV of the Indenture
shall apply to the obligations of the Guarantor under this Guarantee as if (x)
such Article XV were set forth herein in full and (y) such obligations were
substituted for the term "Securities" appearing in such Article XV, (ii) pari
passu with the Debentures, the Other Debentures and with the most senior
preferred or preference stock now or hereafter issued by the Guarantor and with
any Other Guarantee (as defined herein) and any guarantee now or hereafter
entered into by the Guarantor in respect of any preferred or preference stock of
any Affiliate of the Guarantor, and (iii) senior to the Guarantor's common
stock.

                                  ARTICLE VII
                                  TERMINATION

SECTION 7.1    Termination
               -----------

               This Guarantee shall terminate (i) upon full payment of the
Redemption Price of all Trust Preferred Securities, (ii) upon the full payment
of the amounts payable in accordance with the Trust Agreement, or (iii) the
distribution of the Debentures to the Holders of all of the Trust Preferred
Securities. Notwithstanding the foregoing, this Guarantee will continue to be
effective or will be reinstated, as the case may be, if at any time any Holder
must restore payment of any sums paid under the Trust Preferred Securities or
under this Guarantee.

                                 ARTICLE VIII
                COMPENSATION AND EXPENSES OF GUARANTEE TRUSTEE

               The Guarantor covenants and agrees to pay to the Guarantee
Trustee from time to time, and the Guarantee Trustee shall be entitled to, such
compensation as shall be agreed to in writing between the Guarantor and the
Guarantee Trustee (which shall not be limited by any provision of law in regard
to the compensation of a trustee of an express trust), and the Guarantor will
pay or reimburse the Guarantee Trustee upon its request for all reasonable
expenses,

                                       15
<PAGE>

disbursements and advances incurred or made by the Guarantee Trustee in
accordance with any of the provisions of this Guarantee (including the
reasonable compensation and the expenses and disbursements of its counsel and of
all persons not regularly in its employ) except any such expense, disbursement
or advance as may arise from its negligence or bad faith. The Guarantor also
covenants to indemnify each of the Guarantee Trustee (and its officers, agents,
directors and employees) for, and to hold it harmless against, any and all loss,
damage, claim, liability or expense including taxes (other than taxes based on
the income of the Guarantee Trustee) incurred without negligence or bad faith on
the part of the Guarantee Trustee and arising out of or in connection with the
acceptance or administration of this guarantee, including the costs and expenses
of defending itself against any claim of liability in the premises. The
obligations of the Guarantor under this Article VIII to compensate and indemnify
the Guarantee Trustee and to pay or reimburse the Guarantee Trustee for
expenses, disbursements and advances shall be secured by a lien prior to that of
the Trust Preferred Securities upon all property and funds held or collected by
the Guarantee Trustee as such, except funds held in trust for the benefit of the
holders of particular Trust Preferred Securities.

               The provisions of this Article shall survive the termination of
this Guarantee.

                                  ARTICLE IX
                                INDEMNIFICATION

SECTION 9.1    Exculpation
               -----------

               (a)  No Indemnified Person shall be liable, responsible or
accountable in damages or otherwise to the Guarantor or any Covered Person for
any loss, damage or claim incurred by reason of any act or omission performed or
omitted by such Indemnified Person in good faith in accordance with this
Guarantee and in a manner that such Indemnified Person reasonably believed to be
within the scope of the authority conferred on such Indemnified Person by this
Guarantee or by law, except that an Indemnified Person shall be liable for any
such loss, damage or claim incurred by reason of such Indemnified Person's
negligence or willful misconduct with respect to such acts or omissions.

               (b)  An Indemnified Person shall be fully protected in relying in
good faith upon the records of the Guarantor and upon such information,
opinions, reports or statements presented to the Guarantor by any Person as to
matters the Indemnified Person reasonably believes are within such other
Person's professional or expert competence and who has been selected with
reasonable care by or on behalf of the Guarantor, including information,
opinions, reports or statements as to the value and amount of the assets,
liabilities, profits, losses, or any other facts pertinent to the existence and
amount of assets from which Distributions to Holders might properly be paid.

SECTION 9.2    Indemnification
               ---------------

               The Guarantor agrees to indemnify each Indemnified Person for,
and to hold each Indemnified Person harmless against, any and all loss,
liability, damage, claim or expense

                                       16
<PAGE>

incurred without negligence or bad faith on its part, arising out of or in
connection with the acceptance or administration of the trust or trusts
hereunder, including the costs and expenses (including reasonable legal fees and
expenses) of defending itself against, or investigating, any claim or liability
in connection with the exercise or performance of any of its powers or duties
hereunder. The obligation to indemnify as set forth in this Section 9.2 shall
survive the termination of this Guarantee.

                                   ARTICLE X
                                 MISCELLANEOUS

SECTION 10.1   Successors and Assigns
               ----------------------

               All guarantees and agreements contained in this Guarantee shall
bind the successors, assigns, receivers, trustees and representatives of the
Guarantor and shall inure to the benefit of the Holders then outstanding.

SECTION 10.2   Amendments
               ----------

               Except with respect to any changes that do not materially
adversely affect the rights of Holders (in which case no consent of Holders will
be required), this Guarantee may only be amended with the prior approval of the
Holders of a Majority in liquidation amount of the Securities (including the
stated amount that would be paid on redemption, liquidation or otherwise, plus
accrued and unpaid Distributions to the date upon which the voting percentages
are determined). The provisions of the Trust Agreement with respect to consents
to amendments thereof (whether at a meeting or otherwise) shall apply to the
giving of such approval.

SECTION 10.3   Notices
               -------

               All notices provided for in this Guarantee shall be in writing,
duly signed by the party giving such notice, and shall be delivered, telecopied
or mailed by first class mail, as follows:

               (a)  If given to the Trust, in care of the Administrative Trustee
at the Trust's mailing address set forth below (or such other address as the
Trust may give notice of to the Holders and the Guarantee Trustee):

                    AGL Capital Trust II
                    c/o AGL Capital Corporation
                    2325-B Renaissance Drive
                    Las Vegas, Nevada 89119
                    Attention: Paul R. Shlanta

               (b)  If given to the Guarantee Trustee, at the Guarantee
Trustee's mailing address set forth below (or such other address as the
Guarantee Trustee may give notice of to the Holders and the Trust):

                                       17
<PAGE>

                    The Bank of New York
                    101 Barclay Street, 21 West
                    New York, New York 10286
                    Attention: Corporate Trust Trustee Administration

               (c)  If given to the Guarantor, at the Guarantor's mailing
address set forth below (or such other address as the Guarantor may give notice
of to the Holders of the Trust Preferred Securities and the Guarantee Trustee):

                    AGL Resources Inc.
                    817 West Peachtree Street, N.W.
                    Atlanta, Georgia 30308
                    Attention: Richard T. O'Brien

               (d)  If given to any Holder of Trust Preferred Securities, at the
address set forth on the books and records of the Trust.

               All such notices shall be deemed to have been given when received
in person, telecopied with receipt confirmed, or mailed by first class mail,
postage prepaid except that if a notice or other document is refused delivery or
cannot be delivered because of a changed address of which no notice was given,
such notice or other document shall be deemed to have been delivered on the date
of such refusal or inability to deliver.

SECTION 10.4   Benefit
               -------

               This Guarantee is solely for the benefit of the Holders and,
subject to Section 3.1(a), is not separately transferable from the Trust
Preferred Securities.

SECTION 10.5   Governing Law
               -------------

               THIS GUARANTEE SHALL BE GOVERNED BY, AND CONSTRUED AND
INTERPRETED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK, WITHOUT
REGARD TO CONFLICTS OF LAWS PRINCIPLES THEREOF.

                                       18
<PAGE>

               THIS GUARANTEE is executed as of the day and year first above
written.

                         AGL RESOURCES INC.,
                         as Guarantor

                         By:____________________________________________________
                         Name:  Donald P. Weinstein
                         Title: Senior Vice President and Chief Financial
                                Officer

                         THE BANK OF NEW YORK,
                         as Guarantee Trustee

                         By:____________________________________________________
                         Name:
                         Title:

                                       19