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                                                                    EXHIBIT 4.01

                            SOUTHWEST GAS CORPORATION

                                       TO

                        THE BANK OF NEW YORK, AS TRUSTEE

                          FOURTH SUPPLEMENTAL INDENTURE

                             DATED AS OF MAY 6, 2002

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


                         SUPPLEMENTING AND AMENDING THE

                       INDENTURE DATED AS OF JULY 15, 1996

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

                     7.625% SENIOR UNSECURED NOTES DUE 2012


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               FOURTH SUPPLEMENTAL INDENTURE, dated as of May 6, 2002, between
SOUTHWEST GAS CORPORATION, a corporation duly organized and existing under the
laws of the State of California (the "Company"), having its principal office at
5241 Spring Mountain Road, P. O. Box 98510, Las Vegas, Nevada 89193-8510, and
THE BANK OF NEW YORK, a New York banking corporation, as successor to Harris
Trust and Savings Bank, as trustee (the "Trustee").

                             RECITALS OF THE COMPANY

               WHEREAS, the Company and the Trustee have executed and delivered
an Indenture dated as of July 15, 1996 (the "Original Indenture" and, as amended
by the First Supplemental Indenture, as hereinafter defined, the Second
Supplemental Indenture, as hereinafter defined, the Third Supplemental
Indenture, as hereinafter defined, and this Fourth Supplemental Indenture, the
"Indenture") providing for the issuance from time to time by the Company of its
unsecured debentures, notes or other evidences of indebtedness to be issued in
one or more series as provided in the Original Indenture; and

               WHEREAS, the Company has duly authorized the execution and
delivery of a First Supplemental Indenture to the Indenture (the "First
Supplemental Indenture") to provide for the issuance of two series of debentures
known as 7-1/2% Debentures, Due 2006 and 8% Debentures, Due 2026;

               WHEREAS, the Company has duly authorized the execution and
delivery of a Second Supplemental Indenture to the Indenture (the "Second
Supplemental Indenture") to provide for the issuance of a series of medium-term
notes known as Medium-Term Notes, Series A;

               WHEREAS, the Company has duly authorized the execution and
delivery of a Third Supplemental Indenture to the Indenture (the "Third
Supplemental Indenture") to provide for the issuance of a series of notes to be
known as the 8.375% Notes due 2011 (the "2011 Notes"); and

               WHEREAS, the Company has duly authorized the execution and
delivery of this Fourth Supplemental Indenture to the Indenture to provide for
the issuance of a series of notes to be known as the 7.625% Senior Unsecured
Notes due 2012 (the "2012 Notes"); and

               WHEREAS, all things necessary to make this Fourth Supplemental
Indenture a valid agreement of the Company, in accordance with its terms, have
been done.

               NOW, THEREFORE, THIS INDENTURE WITNESSETH:

               For and in consideration of the premises and the purchase of the
2012 Notes by the Holders thereof, it is mutually covenanted and agreed, for the
equal and proportionate benefit of all Holders of the 2012 Notes, as follows:


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                                   ARTICLE ONE
                        DEFINITIONS WITH RESPECT TO NOTES

        Section 1.1. Original Indenture Terms. Except as otherwise provided in
this Fourth Supplemental Indenture, all terms used in this Fourth Supplemental
Indenture which are defined in the Original Indenture, the First Supplemental
Indenture, the Second Supplemental Indenture, or the Third Supplemental
Indenture shall have the meanings assigned to them in the Original Indenture,
the First Supplemental Indenture, the Second Supplemental Indenture, or the
Third Supplemental Indenture, as the case may be.

        Section 1.2. Additional Terms. Additional terms used in this Fourth
Supplemental Indenture with respect to the 2012 Notes shall have the meanings
set forth below:

               "2012 Notes" means the 7.625% Senior Unsecured Notes due 2012
        authenticated and delivered under the Indenture.

               "Fourth Supplemental Indenture" means this fourth supplemental
        indenture dated as of May 6, 2002 as originally executed and as it may
        from time to time be supplemented or amended by one or more indentures
        pursuant to the provisions of the Original Indenture and shall include
        the terms of the 2012 Notes established pursuant to Article Two thereof.

               "Reference Treasury Dealer" means, with respect to the 2012
        Notes, (A) Banc of America Securities LLC or BNY Capital Markets, Inc.
        (or their respective affiliates which are Primary Treasury Dealers), and
        their respective successors; provided, however, that if any of the
        foregoing shall cease to be a primary U.S. Government securities dealer
        in New York City (a "Primary Treasury Dealer"), we will substitute
        therefor another Primary Treasury Dealer; and (B) any other Primary
        Treasury Dealer(s) selected by the Trustee after consultation with us.

        Section 1.3. Modification of Terms. The following defined terms used in
the Original Indenture shall have the following meanings when used with respect
to the 2012 Notes:

               (a) "Redemption Date", when used with respect to a redemption of
        a 2012 Note at the option of the Company pursuant to the Fourth
        Supplemental Indenture, means any date specified as a "Redemption Date"
        in a notice of redemption provided the Holders in accordance with the
        provisions of Article Eleven of the Original Indenture.

               (b) "Redemption Price", when used with respect to the redemption
        of a 2012 Note at the option of the Company on a Redemption Date
        pursuant to the Fourth Supplemental Indenture, means the greater of (i)
        100% of the principal amount of the 2012 Notes being redeemed on such
        Redemption Date, and (ii) the sum of the present values of the remaining
        scheduled payments of principal and interest on the 2012 Notes being
        redeemed on such Redemption Date (not including any portion of any
        payments of interest accrued to such Redemption Date) discounted to such
        Redemption Date on a semi-annual basis at the Adjusted Treasury Rate,
        plus 35 basis points, as determined by the Reference Treasury Dealer,
        plus, in either case, accrued and unpaid interest thereon


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        to, but excluding such Redemption Date, but interest installments whose
        Stated Maturity is on or prior to such Redemption Date will be payable
        on the Interest Payment Date to the Holders of such 2012 Notes, or one
        or more Predecessor Securities, at the close of business on the relevant
        Regular Record Date.

                                   ARTICLE TWO
                               FORM OF 2012 NOTES

        Section 2.1. Form of Face of 2012 Note.

               THIS SECURITY IS A GLOBAL SECURITY WITHIN THE MEANING OF THE
INDENTURE (AS DEFINED ON THE REVERSE HEREOF) AND IS REGISTERED IN THE NAME OF A
DEPOSITARY OR A NOMINEE OF A DEPOSITARY. THIS GLOBAL SECURITY IS EXCHANGEABLE
FOR SECURITIES REGISTERED IN THE NAME OF A PERSON OTHER THAN THE DEPOSITARY OR
ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE, AND NO
TRANSFER OF THIS SECURITY (OTHER THAN A TRANSFER OF THIS SECURITY AS A WHOLE BY
THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY OR BY A NOMINEE OF THE DEPOSITARY
TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY) MAY BE REGISTERED EXCEPT
IN THOSE LIMITED CIRCUMSTANCES. EVERY SECURITY DELIVERED UPON (1) REGISTRATION
OF TRANSFER OF, (2) IN EXCHANGE FOR, OR (3) IN LIEU OF, THIS GLOBAL SECURITY
SHALL BE A GLOBAL SECURITY SUBJECT TO THE FOREGOING, EXCEPT IN THE LIMITED
CIRCUMSTANCES DESCRIBED ABOVE.

               UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED
REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY ("DTC"), A NEW YORK CORPORATION,
TO THE COMPANY OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT,
AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH
OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY
PAYMENT IS TO BE MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY
AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF
FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE
REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

No. ____________                                                       $________

CUSIP No.  ______________


                            SOUTHWEST GAS CORPORATION

                      7.625% SENIOR UNSECURED NOTE DUE 2012

               SOUTHWEST GAS CORPORATION, a California corporation (hereinafter
called the "Company," which term includes any successor corporation under the
Indenture), for value received, hereby promises to pay to Cede & Co. or
registered assigns, the principal sum of


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_______ ($_______) on May 15, 2012 and to pay interest thereon from May 6, 2002,
or from the most recent Interest Payment Date to which interest has been paid or
duly provided for, on May 15 and November 15 in each year, commencing November
15, 2002, at the rate of 7.625% per annum, until the principal hereof shall have
become due and payable, and on any overdue principal and (without duplication
and to the extent that payment of such interest is enforceable under applicable
law) on any overdue interest at the same rate per annum compounded
semi-annually. The amount of interest payable on any Interest Payment Date shall
be computed on the basis of a 360-day year of twelve 30-day months. In the event
that any date on which interest is payable on this Note is not a Business Day,
then payment of interest payable on such date will be made on the next
succeeding day that is a Business Day (and without any interest or other payment
in respect of such delay). The interest so payable, and punctually paid or duly
provided for, on any Interest Payment Date will, as provided in the Indenture,
be paid to the Person in whose name this Note (or one or more Predecessor
Securities) is registered at the close of business on the Regular Record Date
for such interest, which shall be the May 1 or November 1 (whether or not a
Business Day), as the case may be, next preceding such Interest Payment Date.
Any such interest not so punctually paid or duly provided for shall forthwith
cease to be payable to the Holder on such Regular Record Date and may, upon
election by the Company following notice to the Trustee, be paid to the Person
in whose name this Note (or one or more Predecessor Securities) is registered at
the close of business on a Special Record Date for the payment of such Defaulted
Interest to be fixed by the Trustee, by giving notice to Holders of Notes of
this series not less than ten (10) days prior to such Special Record Date and
not less than ten (10) days after the receipt by the Trustee of the notice of
the proposed payment.

               Payment of the principal of and interest on this Note will be
made at the offices or agencies of the Company maintained for that purpose in
New York, New York in such coin or currency of the United States of America as
at the time of payment is legal tender for payment of public and private debts;
provided, however, that at the option of the Company payment of interest may be
made by check mailed to the address of the Person entitled thereto as such
address shall appear in the Securities Register on the Record Date, except that
in the event that this Note is registered in the name of the nominee of a
clearing agency, interest payments will be made in the form of next day funds.

               Reference is hereby made to the additional provisions of this
Note set forth on the reverse hereof, which shall for all purposes have the same
effect as if set forth on the face hereof.

               Unless the certificate of authentication below has been executed
by the Trustee referred to on the reverse hereof, this Note shall not be
entitled to any benefit under the Indenture or be valid or obligatory for any
purpose.

               IN WITNESS WHEREOF, the Company has caused this instrument to be
duly executed under its corporate seal.


Dated:                                             SOUTHWEST GAS CORPORATION


                                                   By
                                                     -------------------------

Attest:

By:
    --------------------------
    Secretary


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        Section 2.2. Form of Reverse of 2012 Note

               This Note is one of a duly authorized issue of obligations of the
Company (herein called the "Notes"), issued and to be issued in one or more
series under an Indenture dated as of July 15, 1996 (the "Indenture"), between
the Company and The Bank of New York, as successor to Harris Trust and Savings
Bank, as Trustee (herein called the "Trustee", which term includes any successor
trustee under the Indenture), as supplemented by the Fourth Supplemental
Indenture dated as of May 6, 2002 between the Company and the Trustee and as
hereafter amended and supplemented. Reference to the Indenture is hereby made
for a statement of the respective rights, limitations of rights, duties and
immunities of the Company, the Trustee and the Holders of the Notes and of the
terms upon which the Notes are, and are to be, authenticated and delivered.

               All or a portion of the Notes are subject to redemption at the
option of the Company upon not less than 30 days' and not more than 60 days'
notice by mail at any time or from time to time at a Redemption Price equal to
the greater of (i) 100% of the principal amount of the Notes being redeemed on
the Redemption Date specified in the notice of redemption, and (ii) the sum of
the present values of the remaining scheduled payments of principal and interest
on the Notes being redeemed on such Redemption Date (not including any portion
of any payments of interest accrued to such Redemption Date discounted to such
Redemption Date on a semi-annual basis at the Adjusted Treasury Rate (as defined
in the Indenture), plus 35 basis points, as determined by the Reference Treasury
Dealer (as defined in the Indenture), plus, in either case, accrued and unpaid
interest thereon to, but excluding such Redemption Date, but interest
installments whose Stated Maturity is on or prior to such Redemption Date will
be payable on the Interest Payment Date to the Holders of such Notes, or one or
more Predecessor Securities, at the close of business on the relevant Regular
Record Date referred to on the face hereof, all as provided in the Indenture.
The Redemption Price will be calculated on the basis of a 360-day year
consisting of twelve 30-day months.

               In the event of redemption of this Note in part only, a new Note
or Notes for the unredeemed portion hereof will be issued in the name of the
Holder hereof upon cancellation.

               In certain circumstances described in the Indenture, the
Company's obligations in respect of the Notes of this series or in respect of
certain covenants made for the benefit of Notes of this series may be discharged
prior to payment upon depositing with the Trustee cash and/or U.S. Government
Obligations in the required amount and upon compliance with certain other
provisions of the Indenture.

               If an Event of Default with respect to Notes of this series
occurs and is continuing, the principal of the Notes of this series may be
declared due and payable in the manner and with the effect provided in the
Indenture.


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               The Indenture contains provisions permitting the Company and the
Trustee, with the consent of the Holders of not less than a majority in
aggregate principal amount of the Notes of each series affected at the time
outstanding, as defined in the Indenture, to execute supplemental indentures for
the purpose of adding any provisions to, changing in any manner, or eliminating
any of the provisions of the Indenture or any supplemental indenture, or for the
purpose of modifying in any manner the rights of the Holders of the Notes;
provided, however, that no supplemental indenture shall (i) extend the fixed
maturity of any Notes of any series, or reduce their principal amount, or reduce
the rate or extend the time of payment of interest thereon, without the consent
of the Holder of each Note so affected, or (ii) reduce the aforesaid percentage
of Notes, the Holders of which are required to consent to any such supplemental
indenture, without the consent of the Holders of each Note then outstanding and
affected thereby. The Indenture also contains provisions permitting the Holders
of a majority in aggregate principal amount of the Notes of any series
outstanding and affected thereby, on behalf of all of the Holders of the Notes
of such series, to waive any past default in the performance of any of the
covenants contained in the Indenture, or established pursuant to the Indenture
with respect to that series, and its consequences, except a default in the
payment of the principal of or interest on any of the Notes of that series. Any
consent or waiver by the registered Holder of this Note (unless revoked as
provided in the Indenture) shall be conclusive and binding upon that Holder and
upon all future Holders and owners of this Note and of any Note issued in
exchange herefor or in place hereof (whether by registration of transfer or
otherwise), irrespective of whether or not any notation of the consent or waiver
is made upon this Note.

               In certain limited circumstances, the Indenture may be amended,
and the rights and obligations of the Company and the rights of the Holders may
be modified, at any time by the Company and the Trustee without notice to or
consent of the Holders.

               No reference herein to the Indenture and no provision of this
Note or of the Indenture shall alter or impair the obligation of the Company,
which is absolute and unconditional, to pay the principal of and interest on
this Note at the times, places and rate, and in the coin or currency, described
herein.

               As provided in the Indenture and subject to certain limitations
set forth therein, the transfer of this Note is registrable in the Securities
Register upon surrender of this Note for registration of transfer at the office
or agency of the Company in any place where the principal of and interest on
this Note are payable, if duly endorsed by, or if accompanied by a written
instrument of transfer (in a form that is satisfactory to the Company and the
Securities Registrar) duly executed by, the Holder hereof or his attorney duly
authorized in writing; thereupon one or more new Notes of this series, of
authorized denominations and like aggregate principal amount, will be issued to
the designated transferee or transferees. The Notes of this series are issuable
only in registered form without coupons in denominations of $1,000 and any
integral multiple thereof. As provided in the Indenture and subject to certain
limitations therein set forth, Notes of this series are exchangeable for other
Notes of this series of a different authorized denomination and like principal
amount, as requested by the Holder surrendering the same. No service charge
shall be made for any such registration of transfer or exchange, but the Company
may require payment of a sum sufficient to cover any tax or other governmental
charge payable in connection therewith to the extent provided in the Indenture.


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               Prior to due presentment of this Note for registration of
transfer, the Company, the Trustee and any agent of the Company or the Trustee
may treat the Person in whose name this Note is registered as the owner hereof
for all purposes, whether or not this Note is overdue, and neither the Company,
the Trustee nor any agent shall be affected by notice to the contrary.

               No recourse shall be had for the payment of the principal of or
the interest on this Note, or for any claim based hereon or on the Indenture,
against any incorporator, shareholder, officer or director, past, present or
future, as such, of the Company or of any predecessor or successor Corporation,
under any rule of law, statute or constitution or by the enforcement of any
assessment or otherwise, all such liability being released by the Holder by
accepting this Note and being likewise waived and released by the terms of the
Indenture.

               All capitalized terms used in this Note that are defined in the
Indenture shall have the meanings assigned to them in the Indenture.

                              [FORM OF ASSIGNMENT]


               For value received, the undersigned hereby sells, assigns and
transfers unto [Please insert Tax Identification Number of Assignee]....

                        --------------------------------
                     [Please print or type name of assignee]


the within Note of Southwest Gas Corporation and does hereby irrevocably
constitute and appoint _____________________________ Attorney to transfer said
Note on the books of the within-named corporation, with full power of
substitution in the premises.

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

        Section 2.3. Form of Trustee's Certificate of Authentication for 2012
Notes.

This is one of the Notes, of the series designated herein, referred to in the
Indenture.

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

THE BANK OF NEW YORK, as Trustee
                                   -----------------------
                                   as Authentication Agent

                                          or

                                   By
                                     ------------------------------
                                     Authorized Officer


                                   By:
                                      --------------------------------
                                      Authorized Officer


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                                  ARTICLE THREE
                               TERMS OF 2012 NOTES

        Section 3.1. Terms of 2012 Notes. Pursuant to the provisions of Section
301 of the Original Indenture, the following terms of the 2012 Notes are hereby
established:

               (a) The title of the 2012 Notes is "7.625% Senior Unsecured Notes
        due 2012".

               (b) The limit upon the aggregate principal amount of the 2012
        Notes that may be authenticated and delivered under the Indenture
        (except for 2012 Notes authenticated and delivered upon registration of
        transfer of, or in exchange for, or in lieu of, other 2012 Notes
        pursuant to Section 304, 305, 306, 906 or 1107 of the Original Indenture
        and except for any 2012 Notes which, pursuant to Section 303 of the
        Original Indenture, are deemed never to have been authenticated and
        delivered hereunder) is $200,000,000, unless the aggregate principal
        amount of the 2012 Notes that may be authenticated and delivered under
        the Indenture is increased pursuant to a Board Resolution and, subject
        to Section 303 of the Indenture, determined in the manner provided in an
        Officer's Certificate prior to the issuance of any additional 2012
        Notes. Any additional 2012 Notes so authorized shall be authenticated
        and delivered in accordance with the procedures set forth in Section 303
        of the Indenture.

               (c) The date on which principal of the 2012 Notes is payable,
        unless earlier accelerated or redeemed pursuant to the Indenture, shall
        be May 15, 2012.

               (d) The rate at which the 2012 Notes shall bear interest shall be
        7.625% per annum.

               (e) Interest on the 2012 Notes will accrue from May 6, 2002. The
        Interest Payment Dates on which interest will be payable on the 2012
        Notes shall be May 15 and November 15, commencing November 15, 2002. The
        Regular Record Dates for the 2012 Notes shall be the May 1 and November
        1,whether or not a Business Day, as the case may be, next preceding such
        Interest Payment Date. In the event that any date on which interest is
        payable on this Note is not a Business Day, then payment of interest
        payable on such date will be made on the next succeeding day that is a
        Business Day (and without any interest or other payment in respect of
        such delay).

               (f) The place or places where the principal of and interest on
        the 2012 Notes shall be payable is the office of the Trustee, initially
        at 2 N. LaSalle Street, Chicago, Illinois 60602, provided that the
        payment of interest may be made at the option of the Company by check
        mailed to the address of the Person entitled thereto as such address
        shall appear in the Security Register on the Regular Record Date or by
        wire transfer to the account designated by such Person entitled thereto.


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               (g) All or any portion of the 2012 Notes are subject to
        redemption at the option of the Company upon not less than 30 days' and
        not more than 60 days' notice by mail at any time or from time to time
        at the Redemption Price.

               (h) The 2012 Notes shall be issued as Global Securities and The
        Depository Trust Company is hereby designated as the Depositary for the
        2012 Notes.

                                  ARTICLE FOUR
                       MODIFICATION OF CERTAIN PROVISIONS
                            OF THE ORIGINAL INDENTURE

        Section 4.1. Restrictions on Liens. Section 1008 of the Indenture shall
be applicable to the 2012 Notes so long as any are outstanding.

        Section 4.2. Restrictions on Sale and Lease-back Transactions. Section
1009 of the Indenture shall be applicable to the 2012 Notes so long as any are
outstanding.

                                  ARTICLE FIVE
                 CONTINUED APPLICABILITY OF REMAINING PROVISIONS
                            OF THE ORIGINAL INDENTURE

        Section 5.1. Continued Applicability. Except as specifically amended,
supplemented or deleted by this Fourth Supplemental Indenture, all provisions of
the Original Indenture shall be applicable for all purposes with respect to the
2012 Notes, and the Original Indenture, as supplemented and amended hereby and
by the First Supplemental Indenture, the Second Supplemental Indenture, and the
Third Supplemental Indenture is hereby ratified, confirmed and approved. The
Original Indenture as supplemented and amended by the First Supplemental
Indenture, the Second Supplemental Indenture, the Third Supplemental Indenture,
and this Fourth Supplemental Indenture shall be construed as one and the same
instrument.


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        IN WITNESS WHEREOF, the parties hereto have caused this Fourth
Supplemental Indenture to be duly executed as of the day and year first above
written.

                                        SOUTHWEST GAS CORPORATION


                                        By /s/Jeffrey W. Shaw
                                           --------------------------------
                                           Jeffrey W. Shaw
                                           Senior Vice President/Treasurer


                                        THE BANK OF NEW YORK, as Trustee



                                        By /s/ Michael Pitsick
                                           --------------------------
                                          Authorized Officer


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