SOUTHWEST GAS CORP
424B2, 1996-08-01
NATURAL GAS TRANSMISISON & DISTRIBUTION
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<PAGE>   1
 
PROSPECTUS SUPPLEMENT
 
(TO PROSPECTUS DATED OCTOBER 24, 1995)
 
                                  $150,000,000                              LOGO
                                                                             (R)
 
                           SOUTHWEST GAS CORPORATION
   
                     $75,000,000 7 1/2% DEBENTURES DUE 2006
    
   
                       $75,000,000 8% DEBENTURES DUE 2026
    
                            ------------------------
 
   
     The 7 1/2% Debentures Due 2006 (the "7 1/2% Debentures") mature on August
1, 2006 and the 8% Debentures Due 2026 (the "8% Debentures" and, together with
the 7 1/2% Debentures, the "Debentures") mature on August 1, 2026. Interest on
the Debentures is payable semi-annually on February 1 and August 1 of each year,
beginning February 1, 1997. The Debentures are not redeemable prior to maturity.
    
 
   
     Each series of Debentures will be represented by a Global Debenture
registered in the name of Cede & Co., as nominee for The Depository Trust
Company (the "Depository"). Beneficial interests in the Global Debentures will
be shown on records maintained by, transfers thereof will be effected only
through, and payment of principal of and interest on Debentures will be made
only through, the Depository, and with respect to the beneficial owners'
interests, by the Depository's participants. Except as described herein,
Debentures in definitive form will not be issued. See "Description of
Debentures -- Global Debentures." Settlement for the Debentures will be in
immediately available funds.
    
                            ------------------------
 
THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES
   AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS
      THE SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES
        COMMISSION PASSED UPON THE ACCURACY OR ADEQUACY OF THIS
         PROSPECTUS SUPPLEMENT OR THE PROSPECTUS. ANY
   
           REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.
 
<TABLE>
<S>                        <C>                        <C>                        <C>
- -----------------------------------------------------------------------------------------------------------
- -----------------------------------------------------------------------------------------------------------
                                                             UNDERWRITING             PROCEEDS TO THE
                               PRICE TO PUBLIC(1)            DISCOUNT(2)               COMPANY(1)(3)
- -----------------------------------------------------------------------------------------------------------
Per 7 1/2% Debenture......          99.176%                      .65%                     98.526%
- -----------------------------------------------------------------------------------------------------------
          Total...........        $74,382,000                  $487,500                 $73,894,500
- -----------------------------------------------------------------------------------------------------------
Per 8% Debenture..........          99.682%                     .875%                     98.807%
- -----------------------------------------------------------------------------------------------------------
          Total...........        $74,761,500                  $656,250                 $74,105,250
- -----------------------------------------------------------------------------------------------------------
- -----------------------------------------------------------------------------------------------------------
</TABLE>
    
 
   
(1) Plus accrued interest from August 1, 1996.
    
 
(2) The Company has agreed to indemnify the Underwriters against certain
    liabilities under the Securities Act of 1933, as amended. See
    "Underwriting."
 
(3) Before deducting expenses payable by the Company estimated at $200,000.
                            ------------------------
 
   
     The Debentures are being offered by the Underwriters, subject to prior
sale, when, as and if delivered to and accepted by it, subject to approval of
certain legal matters by counsel for the Underwriters and certain other
conditions. The Underwriters reserve the right to withdraw, cancel or modify
such offer and reject orders in whole or in part. It is expected that delivery
of the Debentures will be made through the facilities of the Depository on or
about August 5, 1996, against payment therefor in immediately available funds.
    
                            ------------------------
 
MERRILL LYNCH & CO.                                     PAINEWEBBER INCORPORATED
                            ------------------------
 
   
            The date of this Prospectus Supplement is July 31, 1996.
    
<PAGE>   2
 
     IN CONNECTION WITH THIS OFFERING, THE UNDERWRITERS MAY OVER-ALLOT OR EFFECT
TRANSACTIONS WHICH STABILIZE OR MAINTAIN THE MARKET PRICE OF THE SECURITIES
OFFERED HEREBY AT A LEVEL ABOVE THAT WHICH MIGHT OTHERWISE PREVAIL IN THE OPEN
MARKET. SUCH STABILIZING, IF COMMENCED, MAY BE DISCONTINUED AT ANY TIME.
 
                                  THE COMPANY
 
     Southwest Gas Corporation (the "Company") is the largest distributor of
natural gas in Arizona, distributing and transporting natural gas in most of
southern, central, and northwestern Arizona including the Phoenix and Tucson
metropolitan areas. The Company is also the largest distributor and transporter
of natural gas in Nevada, and serves the Las Vegas metropolitan area and
northern Nevada. In addition, the Company distributes and transports natural gas
in portions of California, including the Lake Tahoe area in northern California
and high desert and mountain areas of San Bernardino County in southern
California.
 
     During the twelve months ended March 31, 1996, the contribution to total
natural gas operating margin from each of the Company's major geographic
operations areas was as follows: Arizona -- 57 percent, Nevada -- 32 percent and
California -- 11 percent. During the same period, the Company earned 59 percent
of operating margin from residential customers, 24 percent from commercial
customers, and 17 percent from industrial and other customers. These patterns
are consistent with prior years and are expected to continue.
 
     At December 31, 1995, approximately 605,000 (or 59 percent) of the
Company's natural gas customers were in Arizona, 317,000 (or 31 percent) were in
Nevada and 107,000 (or 10 percent) were in California. A federal Census Bureau
report for the year ended July 1, 1994 showed that Nevada and Arizona ranked
first and second, respectively, in terms of percentage population growth.
Customer growth in the Company's three-state territory was 35,000 in 1993,
48,000 in 1994 and 49,000 in 1995. Customer growth over the past three years
averaged five percent annually. Based on commitments from builders, the Company
expects customer growth to approximate five percent during 1996.
 
     For the twelve months ended March 31, 1996, the Company's natural gas
construction expenditures totaled $171 million, an 18 percent increase over the
$145 million of construction expenditures incurred during the same period a year
ago. The increase is primarily attributed to the investment in new transmission
and distribution plant in Arizona, Nevada and California to meet the demand from
the Company's growing customer base. During the three-year period ended March
31, 1996, the Company's total investment in gas plant in service has increased
from $1.3 billion to $1.6 billion, or at an annual growth rate of eight percent.
The Company currently estimates that annual construction expenditures for the
three-year period ending December 31, 1998 will be approximately $470 million.
See "Capital Expenditures and Financing Programs."
 
     The Company is authorized to charge its distribution system customers rates
determined by the Arizona Corporation Commission, the California Public
Utilities Commission and the Public Service Commission of Nevada (the "PSCN") in
general rate cases, which rates are derived using rate base, cost of service and
cost of capital experienced in an adjusted historical test year in Arizona and
Nevada, and in a projected future test year in California. The Federal Energy
Regulatory Commission regulates the northern Nevada transmission system and the
liquefied natural gas storage facilities of Paiute Pipeline Company ("Paiute"),
a wholly owned subsidiary of the Company, as well as the rates Paiute charges
for transportation of gas directly to certain end-users and to various local
distribution companies.
 
     In December 1995, the Company filed general rate cases for its two Nevada
jurisdictions with the PSCN. In April 1996, the PSCN approved a settlement of
the general rate cases that provided the Company with a $10.6 million general
rate increase in southern Nevada and a $3.2 million increase in northern Nevada.
The settlement achieved a number of rate design and tariff restructuring changes
resulting in rates that are more cost-based. Over 86 percent of annual margin in
Nevada will now be recoverable from core customer classes, those most
responsible for the increased costs of operations. The settlement also adjusts
rate design by equalizing margins earned from sales and transportation
customers, resulting in consistent margin regardless of
 
                                       S-2
<PAGE>   3
 
the type of service elected by a customer. The settlement also specifies a
moratorium on future general rate increase requests until April 1999. The new
rates became effective July 1, 1996.
 
     The Company plans to file for additional rate relief in its Arizona
jurisdictions no later than the fourth quarter of 1996, with new rates expected
to be in effect approximately twelve months after filing. Its current rate
settlement for its California jurisdictions, effective January 1995, will remain
in effect through 1998. The Company's rate schedules in all of its distribution
service areas contain purchased gas adjustment clauses which permit the Company
to adjust its rates periodically as the cost of purchased gas changes.
 
                              RECENT DEVELOPMENTS
 
     In January 1996, the Company entered into an agreement to sell all of the
outstanding common stock of its wholly owned subsidiary PriMerit Bank
("PriMerit" or the "Bank") to Norwest Corporation. In April 1996, Norwest
elected to structure the acquisition as a purchase of substantially all of the
assets and liabilities of the Bank, rather than a stock purchase, pursuant to an
option in the original agreement.
 
     On July 19, 1996, the Company completed the sale of PriMerit. In accordance
with the agreement, Norwest paid the Company $191 million in cash for
substantially all of the assets and liabilities of PriMerit, other than certain
assets and liabilities relating to taxes and real estate development activities
formerly conducted by the Bank and certain recorded intangibles. Net proceeds of
approximately $163 million, after payment of income taxes and other costs
associated with the sale, will be used to reduce outstanding long-term debt (see
"Capitalization").
 
     On November 13, 1995, the Company and Northern Pipeline Construction Co.
("NPL") entered into a definitive agreement calling for the acquisition of 100
percent of the outstanding stock of NPL for $24 million in common stock of the
Company. On April 29, 1996, the Company completed the acquisition of NPL. In
connection therewith, 1,439,280 new shares of the Company's common stock were
issued to the NPL stockholders.
 
     NPL, headquartered in Phoenix, Arizona, provides gas distribution companies
(including the Company) with installation, replacement and maintenance services
for underground natural gas distribution systems. The principal focus of
business operations centers around main and service line replacement and new
business installation of mains and services. NPL operates in numerous locations
throughout the United States.
 
     On July 16, 1996, the Company's stockholders approved an amendment to the
Restated Articles of Incorporation of the Company to increase the authorized
shares of the Company's common stock from 30,000,000 shares to 45,000,000
shares.
 
                      RATIOS OF EARNINGS TO FIXED CHARGES
 
     The following table sets forth the ratios of earnings to fixed charges for
(a) the continuing operations of the Company and (b) the continuing operations
of the Company adjusted for interest allocated to the discontinued operations of
PriMerit.
 
<TABLE>
<CAPTION>
                                                                            FOR THE YEAR ENDED
                                                   FOR THE TWELVE              DECEMBER 31,
                                                    MONTHS ENDED    ----------------------------------
                                                   MARCH 31, 1996   1995     1994   1993   1992   1991
                                                   --------------   ----     ----   ----   ----   ----
<S>                                                <C>              <C>      <C>    <C>    <C>    <C>
Ratios of earnings to fixed charges(1):
  Continuing operations..........................       1.07(2)     1.06(2)  1.69   1.47   2.21   1.70
  Adjusted for interest allocated to discontinued
     operations..................................       1.06(2)     1.05(2)  1.61   1.40   2.03   1.61
</TABLE>
 
- ---------------
(1) For purposes of computing the ratios of earnings to fixed charges, earnings
    are defined as the sum of pretax income from continuing operations plus
    fixed charges. Fixed charges consist of all interest expense including
    capitalized interest, one-third of rent expense (which approximates the
    interest component of such expense) and amortized debt costs.
 
(2) These ratios were impacted by record warm weather during the 1995 and first
    quarter 1996 heating seasons. See Note (1) to "Selected Financial
    Information."
 
                                       S-3
<PAGE>   4
 
                         SELECTED FINANCIAL INFORMATION
 
     The following selected financial information for each of the three years in
the period ended December 31, 1995 is derived from the Company's 1995 Annual
Report on Form 10-K. The selected financial information for the twelve-month
period ended March 31, 1996 is derived from the Company's first quarter 1996
Quarterly Report on Form 10-Q. The Company's consolidated financial statements
in the 1995 Annual Report on Form 10-K have been audited by Arthur Andersen LLP,
independent public accountants. The selected financial information set forth
below should be read in conjunction with the detailed information, consolidated
financial statements and related notes and applicable management's discussion
and analysis included in the 1995 Annual Report on Form 10-K and the Company's
first quarter 1996 Quarterly Report on Form 10-Q, which are incorporated herein
by reference.
 
<TABLE>
<CAPTION>
                                           TWELVE MONTHS             YEAR ENDED DECEMBER 31,
                                          ENDED MARCH 31,     --------------------------------------
                                               1996              1995           1994          1993
                                          ---------------     ----------     ----------     --------
                                               (DOLLARS IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
<S>                                       <C>                 <C>            <C>            <C>
CONSOLIDATED INCOME STATEMENT DATA:
Operating revenues......................    $   548,333       $  563,502     $  599,553     $539,105
Operating expenses......................        488,211          505,090        510,863      461,423
                                            -----------       ----------     ----------     --------
Operating income........................    $    60,122       $   58,412     $   88,690     $ 77,682
                                            ===========       ==========     ==========     ========
Income from continuing operations.......    $     3,064(1)    $    2,654(1)  $   23,524     $ 13,751(2)
Income (loss) from discontinued
  operations, net of tax(3).............        (17,732)         (17,536)         2,777        1,655
                                            -----------       ----------     ----------     --------
Net income (loss).......................    $   (14,668)      $  (14,882)    $   26,301     $ 15,406
                                            ===========       ==========     ==========     ========
Net income (loss) applicable to common
  stock.................................    $   (14,880)      $  (15,189)    $   25,791     $ 14,665
                                            ===========       ==========     ==========     ========
Earnings (loss) per share
  Continuing operations.................    $      0.12       $     0.10     $     1.09     $   0.63
  Discontinued operations...............          (0.74)           (0.76)          0.13         0.08
                                            -----------       ----------     ----------     --------
Earnings (loss) per share...............    $     (0.62)      $    (0.66)    $     1.22     $   0.71
                                            ===========       ==========     ==========     ========
Dividends paid per common share.........    $      0.82       $     0.82     $     0.80     $   0.74
Weighted average number of shares of
  common stock outstanding (000's)......         24,025           23,167         21,078       20,729
NATURAL GAS SEGMENT DATA:
Operating margin........................    $   341,314(1)    $  336,046(1)  $  349,631     $326,815
Construction expenditures...............        171,029          166,183        141,390      113,903
Net gas utility property (end of
  period)...............................      1,159,416        1,137,750      1,035,916      954,488
Number of customers (end of period).....      1,042,000        1,029,000        980,000      932,000
</TABLE>
 
- ---------------
(1) Record warm weather during the first and fourth quarters of 1995 and the
    first quarter of 1996 significantly impacted operating margin. The Company
    estimates that, on a weather-normalized basis, before income taxes, 1995
    operating margin would have been approximately $28 million greater, and
    operating margin for the twelve months ended March 31, 1996 would have been
    approximately $29 million greater than actually reported.
 
(2) In 1993, the Company wrote off $15.9 million in gross plant related to its
    central and southern Arizona pipe replacement programs. The impact of this
    disallowance, net of accumulated depreciation, tax benefits and other
    related items, was a non-cash reduction to consolidated net income of $9.3
    million, or $0.44 per share.
 
(3) In January 1996, the Company entered into an agreement to sell all of the
    outstanding common stock of the Bank to Norwest Corporation, and as such,
    the Bank is reported as discontinued operations. The amounts shown as
    discontinued operations consist of income (loss) from the Bank's stand-alone
    income statements adjusted for corporate carrying costs allocated to the
    Bank and loss on disposal of the discontinued segment.
 
                                       S-4
<PAGE>   5
 
                                 CAPITALIZATION
 
     The capitalization and short-term debt of the Company and its consolidated
subsidiaries as of March 31, 1996, as adjusted to give effect to the acquisition
of NPL in April 1996, the use of proceeds from the disposition of PriMerit in
July 1996, and the issuance of the Debentures offered hereby and the application
of the net proceeds therefrom, after deducting the underwriting discount and
estimated offering expenses, are as follows:
 
   
<TABLE>
<CAPTION>
                                            AS OF                                                   AS OF
                                        MARCH 31, 1996                ADJUSTMENTS               MARCH 31, 1996
                                      ------------------     ------------------------------   ------------------
                                        ACTUAL       %         (1)        (2)        (3)       ADJUSTED      %
                                      ----------   -----     -------   ---------   --------   ----------   -----
                                                                (DOLLARS IN THOUSANDS)
<S>                                   <C>          <C>       <C>       <C>         <C>        <C>          <C>
CAPITALIZATION
Long-term debt:
Debentures:
  Series A, 9% due 2011.............  $   26,838                                   $(26,838)
  Series B, 9% due 2011.............      31,168                                    (31,168)
  Series C, 8.75% due 2011..........      18,323                                    (18,323)
  Series D, 9.375% due 2017.........     120,000                       $ (59,000)   (61,000)
  Series E, 10% due 2013............      23,069                         (23,069)
  Series F, 9.75% due 2002..........     100,000                                              $  100,000
  7 1/2% due 2006...................                                                 75,000       75,000
  8% due 2026.......................                                                 75,000       75,000
                                      ----------                       ---------   --------   ----------
    Total debentures................     319,398                         (82,069)    12,671      250,000
  Less: unamortized discount........      (6,103)                                                 (6,103)
                                      ----------                       ---------   --------   ----------
    Net debentures..................     313,295                         (82,069)    12,671      243,897
Other long-term debt................     419,371                         (37,931)                381,440
                                      ----------                       ---------   --------   ----------
  Total long-term debt..............     732,666                        (120,000)    12,671      625,337
  Less: current maturities..........    (120,000)                        120,000
                                      ----------                       ---------   --------   ----------
                                         612,666    58.7%                      0     12,671      625,337    57.9%
                                      ----------                       ---------   --------   ----------
Company-obligated mandatorily
  redeemable preferred securities of
  Southwest Gas Capital I...........      60,000     5.8%                                         60,000     5.6%
                                      ----------                                              ----------
Stockholders' equity:
  Common stock and additional paid
    in capital......................     343,075             $24,000                             367,075
  Retained earnings.................      27,084                                                  27,084
                                      ----------             -------                          ----------
Total stockholders' equity..........     370,159    35.5%     24,000                             394,159    36.5%
                                      ----------   -----     -------   ---------   --------   ----------   -----
Total capitalization................  $1,042,825   100.0%    $24,000   $       0   $ 12,671   $1,079,496   100.0%
                                      ==========   =====     ========  ==========  =========  ==========   =====
</TABLE>
    
 
- ---------------
(1) As described in this Prospectus Supplement, on April 29, 1996, the Company
    acquired NPL for $24 million of the Company's common stock.
 
(2) As described in this Prospectus Supplement, on July 19, 1996, the sale of
    PriMerit to Norwest Corporation was completed. In connection therewith, the
    Company received $191 million in cash. Of this amount, approximately $26
    million will be used to pay income taxes and other costs associated with the
    sale; $120 million will be used to repay long-term debt (which includes
    Series E and a portion of the D debentures); and the remaining $43 million
    will be used to repay short-term borrowings which have been incurred since
    March 31, 1996.
 
(3) Reflects an adjustment for the sale of the Debentures. The net proceeds from
    the sale of the Debentures are assumed to be used to repay outstanding
    debentures that are currently callable, and for general corporate purposes.
 
                                       S-5
<PAGE>   6
 
                                USE OF PROCEEDS
 
     Net proceeds from the sale of the Debentures will be used to refund
outstanding callable debentures (including principal and prepayment premiums for
the Series A, B, C, and the remainder of Series D) with the remaining amount to
be used for general corporate purposes, including the acquisition of property
for the construction, completion, extension or improvement of the Company's
pipeline systems and facilities located in and around the communities it serves.
The weighted average cost of the debentures to be refunded at March 31, 1996 was
10.65 percent.
 
                  CAPITAL EXPENDITURES AND FINANCING PROGRAMS
 
     During the three-year period ended December 31, 1995, the Company's gas
segment customer base has grown at an annual average rate of approximately five
percent. The Company anticipates a projected average annual customer growth rate
of approximately five percent over the next three years.
 
     The Company currently estimates that construction expenditures for its
natural gas operations for the three-year period ending December 31, 1998 will
be approximately $470 million. It is currently estimated that cash flow from
operating activities (net of dividends) will generate approximately one-half of
the gas operations total construction expenditures during the three-year period
ending December 31, 1998. A portion of the construction expenditure funding will
be provided by $36 million of funds held in trust, at December 31, 1995, from
the issuance of 1993 Clark County, Nevada, Series A and 1993 City of Big Bear,
California, Series A industrial development revenue bonds. The remaining
requirements are expected to be provided by external financing sources,
including a portion of the proceeds from this transaction.
 
                           DESCRIPTION OF DEBENTURES
 
     The Debentures will be issued under an Indenture, dated as of July 15, 1996
(the "Original Indenture"), between the Company and Harris Trust and Savings
Bank, as Trustee (the "Trustee"), as supplemented and amended by the First
Supplemental Indenture dated as of August 1, 1996 (the "First Supplement," and
the Original Indenture as so supplemented and amended being referred to as the
"Indenture"). The following summaries set forth certain general terms of the
Debentures and are subject to the detailed provisions of the Indenture; whenever
particular provisions of the Indenture or the First Supplement are referred to,
such provisions are incorporated herein by reference as part of the statement
made and such statement is qualified in its entirety by such reference.
Capitalized terms that are used and not otherwise defined herein shall have
meanings assigned to them in the Indenture. Additional information regarding the
Debentures is set forth in the accompanying Prospectus under the caption
"Description of Debt Securities."
 
GENERAL
 
   
     The 7 1/2% Debentures and 8% Debentures will each be limited in principal
amount to $75,000,000. The Debentures will bear interest from August 1, 1996, or
from the most recent Interest Payment Date to which interest has been paid at
the rates of interest set forth on the cover page hereof. Interest will be
payable semiannually on February 1 and August 1, commencing February 1, 1997, to
the persons in whose name the Debentures are registered at the close of business
on the January 15 or July 15 next preceding such interest payment date. For so
long as the Debentures are registered in the name of the Depository, or its
nominee, the principal and interest due on the Debentures will be payable by the
Company or its agent to the Depository for payment to its Participants (as
defined herein) for subsequent disbursement to the beneficial owners. Interest
will be computed on the basis of a 360-day year of twelve 30-day months. The
Debentures will mature on the dates shown on the cover page hereof. The
Debentures are not redeemable prior to maturity. (Sections 307 and 310 of the
Indenture and Sections 2.1 and 2.2 of the First Supplement.)
    
 
     The Debentures will not contain risk provisions designed to require the
Company to redeem the Debentures, reset the interest rate or take other actions
in response to a change in control, highly leveraged transaction, change in
credit rating or other similar occurrences involving the Company that may
adversely affect the Holders of the Debentures.
 
                                       S-6
<PAGE>   7
 
UNSECURED OBLIGATIONS
 
     The Debentures will be unsecured general obligations of the Company and
will rank on a parity with all other unsubordinated, unsecured indebtedness of
the Company. There will be no limitations on the amount of indebtedness which
may rank on a parity with the Debentures or on the amount of indebtedness that
may be incurred, or capital stock that may be issued, by the Company.
 
COVENANTS
 
   
     Restrictions on Liens. The Company will not, at any time during which any
Debentures are Outstanding, issue, assume or guarantee any Debt, secured by any
Lien upon any property or asset of the Company (whether such property or asset
is now owned or hereafter acquired), without in any such case effectively
securing, prior to or concurrently with the issuance, assumption or guarantee of
any such Debt, the Debentures (together with, if the Company shall so determine,
any other indebtedness of or guarantee by the Company ranking equally with the
Debentures and then existing or thereafter created) equally and ratably with
(or, at the Company's option, prior to) such Debt. The foregoing restrictions do
not apply to or prevent the creation of: (i) Liens on any property acquired,
constructed or improved by the Company after August 1, 1996 that are created or
assumed contemporaneously with, or within 120 days after, such acquisition or
completion of the construction or improvement, or within six months thereafter
pursuant to a firm commitment for financing arranged with a lender or investor
within such 120-day period, to secure or provide for the payment of all or any
part of the purchase price of such property or the cost of such construction or
improvement incurred after August 1, 1996, or, in addition to Liens referred to
in clauses (ii) and (iii), Liens on any property existing at the time of
acquisition thereof, provided that the Liens do not apply to any property
theretofore owned by the Company other than, in the case of any such
construction or improvement, any theretofore unimproved property on which the
property so constructed or the improvement is located; (ii) existing Liens on
any property or indebtedness of a Corporation that is merged with or into or
consolidated with the Company, provided that the Liens do not apply to any
property theretofore owned by the Company; (iii) Liens in favor of the United
States, any state, or any foreign country or any department, agency or
instrumentality or political subdivision of any such jurisdiction to secure
partial, progress, advance or other payment pursuant to any contract or statute
or to secure any indebtedness incurred for the purpose of financing all or any
part of the purchase price or cost of constructing or improving the property
subject to such Liens, including, without limitation, Liens to secure Debt of
the pollution control or industrial revenue bond type; (iv) Liens on current
assets of the Company to secure loans to the Company which mature within 12
months from the creation thereof and which are made in the ordinary course of
business; (v) Liens on any property (including any natural gas, oil or other
mineral property) of the Company to secure all or part of the cost of
exploration or drilling for or development of oil or gas reserves or laying a
pipeline or to secure Debt incurred to provide funds for any such purpose; (vi)
any Lien existing on August 1, 1996; (vii) Liens on moneys or U.S. Government
Obligations deposited with the Trustee pursuant to the provisions of the
Indenture summarized under "Defeasance" in the accompanying Prospectus; and
(viii) Liens for the sole purpose of extending, renewing or replacing, in whole
or in part, Liens securing Debt of the type referred to in the foregoing clauses
or this clause (viii), provided, however, that the principal amount of Debt so
secured at the time of such extension, renewal or replacement may not be
increased, and that such extension, renewal or replacement is limited to all or
part of the property or indebtedness which secured the Lien so extended, renewed
or replaced (plus improvements on such property).
    
 
   
     Notwithstanding the foregoing, the Company may issue, assume or guarantee
Debt secured by a Lien, which would otherwise be subject to the restrictions
described in the first paragraph of this subsection up to an aggregate amount
that, together with all other Indebtedness of the Company (other than the Debt
secured by Liens described in clauses (i) through (viii) of the first paragraph
of this subsection) that would otherwise be subject to the foregoing
restrictions and the Value of all Sale and Lease-back Transactions existing at
that time (other than any Sale and Lease-back Transaction that, if it had been a
Lien, would have been permitted under clause (i) of the first paragraph of this
subsection and other than Sale and Lease-back Transactions as to which
application of amounts have been made in accordance with clause (ii) of "--
Restrictions on Sale and Lease-back Transactions"), does not at the time exceed
10% of Total Capitalization. (Section 3.1 of the First Supplement)
    
 
                                       S-7
<PAGE>   8
 
   
     Restrictions on Sale and Lease-back Transactions. The Company will not, at
any time during which any Debentures are Outstanding, enter into any Sale and
Lease-back Transaction unless the proceeds from such sale are at least equal to
the fair value of the property being sold and leased-back and either: (i) the
Company is entitled under the provisions described in the preceding paragraph to
incur Debt secured by a Lien on such property without equally and ratably
securing the Debentures; or (ii) the Company, within 120 days of the effective
date of the Sale and Lease-back Transaction (or in the case of clause (A) below,
within six months thereafter pursuant to a firm purchase commitment entered into
within such 120-day period), applies, or covenants that it will apply, an amount
not less than the fair value of such property to one or more of (A) the optional
redemption of Securities issued under the Indenture in accordance with the
provisions thereof and the terms of such Securities to be so redeemed or the
purchase and retirement of Securities as provided pursuant to the Indenture, (B)
the payment or other retirement of Funded Debt which is senior to or on parity
with the Debentures (other than Funded Debt owned by the Company) or (C) the
purchase of other property at not more than its fair value (other than the
property of the company involved in such sale). (Section 3.2 of the First
Supplement)
    
 
     Certain Definitions. The terms set forth below are defined in the Indenture
as follows:
 
          "CAPITALIZED LEASE" means any lease of any property of the Company
     (whether real, personal or mixed) by the Company as lessee that would, in
     conformity with generally accepted accounting principles, be required to be
     accounted for as a capital lease on the balance sheet of the Company.
 
          "CORPORATION" means a corporation, association, company, joint-stock
     company or business trust.
 
          "DEBT" means debt issued, assumed or guaranteed by the Company for
     money borrowed.
 
          "FUNDED DEBT" means all Indebtedness of the Company that by its terms
     or by the terms of any instrument or agreement relating thereto matures
     more than one year from, or is directly or indirectly renewable or
     extendable at the option of the Company to a date more than one year from
     the date of creation thereof (including an option of the Company under a
     revolving credit or similar agreement obligating the lender or lenders to
     extend credit over a period of one year or more), but excluding any
     payments due under the terms thereof within 12 months of any date of
     determination (including any deposit or payment required to be made under
     any repayment provision, sinking fund, purchase fund or similar provision).
 
   
          "INDEBTEDNESS" means, as applied to any Person, Capitalized Leases,
     bonds, notes, debentures and other securities representing obligations for
     borrowed money created or assumed by such Person. All indebtedness
     guaranteed as to payment of principal in any manner by such Person or in
     effect guaranteed by such Person through a contingent agreement to purchase
     such indebtedness, and all indebtedness secured by a Lien upon property
     owned by such Person and upon which such Person customarily pays interest,
     even though such Person has not assumed or become liable for the payment of
     such indebtedness, shall for all purposes thereof be deemed to be
     "Indebtedness" of such Person.
    
 
          "LIEN" means any lien, mortgage, pledge, security interest, charge or
     other encumbrance of any kind.
 
          "PERSON" means any individual, Corporation, limited liability company,
     partnership, joint venture, trust, unincorporated organization or
     government or any agency or political subdivision thereof.
 
          "SALE AND LEASE-BACK TRANSACTION" means any arrangement with any
     Person providing for the lease to the Company of any property of the
     Company (except for temporary leases for a term, including any renewal
     thereof, of not more than three years), which property has been or is to be
     sold or transferred by the Company to such Person.
 
          "TOTAL CAPITALIZATION" means, as at any time, the aggregate of (i) all
     amounts outstanding on such date classified as shareholders' equity of the
     Company on such date, (ii) all amounts outstanding on such date classified
     as preferred or preference stock of the Company on such date and (iii) all
     amounts of Funded Debt of the Company outstanding on such date determined
     on an unconsolidated basis.
 
          "U.S. GOVERNMENT OBLIGATIONS" means securities which are (i) direct
     obligations of the United States of America for the payment of which its
     full faith and credit is pledged, or (ii) obligations of a
 
                                       S-8
<PAGE>   9
 
     Person controlled or supervised by and acting as an agency or
     instrumentality of the United States of America the payment of which is
     unconditionally guaranteed as a full faith and credit obligation by the
     United States of America, which, in either case, are not callable or
     redeemable at the option of the issuer thereof, and shall also include a
     depository receipt issued by a bank or trust company as custodian with
     respect to any such U.S. Government Obligations or a specific payment of
     interest on or principal of any such U.S. Government Obligations held by
     such custodian for the account of the holder of a depository receipt,
     provided that (except as required by law) such custodian is not authorized
     to make any deduction from the amount payable to the holder of such
     depository receipt, in respect of the U.S. Government Obligations, or from
     any amount received by the custodian, in respect of the U.S. Government
     Obligations or the specific payment of interest on or principal of the U.S.
     Government Obligations evidenced by such depository receipt.
 
   
          "VALUE" means, with respect to a Sale and Lease-back Transaction, as
     of any particular time, the amount equal to the greater of: (i) the net
     proceeds from the sale or transfer of the property leased pursuant to such
     Sale and Lease-back Transaction; and (ii) the fair value, in the opinion of
     the board of directors of the Company, of such property at the time of
     entering into such Sale and Lease-back Transaction, in either case divided
     first by the number of full years of the term of the lease and then
     multiplied by the number of full years of such term remaining at the time
     of determination, without regard to any renewal or extension options
     contained in the lease.
    
 
GLOBAL DEBENTURES
 
   
     This discussion of The Depository Trust Company ("DTC") and its book-entry
system supplements the discussion of depository arrangements in "Description of
Debt Securities -- Book-Entry Debt Securities" in the accompanying Prospectus.
    
 
     DTC will act as securities depository for the Debentures. The Debentures
will be issued in fully-registered form in the name of Cede & Co. (DTC's
partnership nominee). One Debenture certificate will be issued as a Global
Debenture for each series of Debentures, in the aggregate principal amount of
each series of Debentures, and will be deposited with DTC.
 
     DTC is a limited-purpose trust company organized under the New York Banking
Law, a "banking organization" within the meaning of the New York Banking Law, a
member of the Federal Reserve System, a "clearing corporation" within the
meaning of the New York Uniform Commercial Code, and a "clearing agency"
registered pursuant to the provisions of Section 17A of the Securities Exchange
Act of 1934. DTC holds securities that its participants ("Direct Participants")
deposit with DTC. DTC also facilitates the settlement among Direct Participants
of securities transactions, such as transfers and pledges, in deposited
securities through electronic computerized book-entry changes in Direct
Participants' accounts, thereby eliminating the need for physical movement of
securities certificates. Direct Participants include securities brokers and
dealers, banks, trust companies, clearing corporations, and certain other
organizations. DTC is owned by a number of its Direct Participants and by the
New York Stock Exchange, Inc., the American Stock Exchange, Inc., and the
National Association of Securities Dealers, Inc. Access to the DTC system is
also available to others such as securities brokers and dealers, banks, and
trust companies that clear through or maintain a custodial relationship with a
Direct Participant, either directly or indirectly ("Indirect Participants" and
together with Direct Participants, "Participants"). The Rules applicable to DTC
and its Participants are on file with the Securities and Exchange Commission.
 
     Purchases of Debentures under the DTC system must be made by or through
Direct Participants, which will receive a credit for the Debentures on DTC's
records. The ownership interest of each actual purchaser of Debentures
("Beneficial Owner") is in turn to be recorded on the Participants' records.
Beneficial Owners will not receive written confirmation from DTC of their
purchase, but Beneficial Owners are expected to receive written confirmations
providing details of the transaction, as well as periodic statements of their
holdings, from the Participant through which the Beneficial Owner entered into
the transaction. Transfers of ownership interests in the Debentures are to be
accomplished by entries made on the books of Participants acting on behalf of
Beneficial Owners. Beneficial Owners will not receive certificates representing
their ownership interests in Debentures, except in the event that use of the
book-entry system for the Debentures is discontinued.
 
                                       S-9
<PAGE>   10
 
     To facilitate subsequent transfers, all Debentures deposited by Direct
Participants with DTC are registered in the name of DTC's partnership nominee,
Cede & Co. The deposit of Debentures with DTC and their registration in the name
of Cede & Co. effect no change in beneficial ownership. DTC has no knowledge of
the actual Beneficial Owners of the Debentures; DTC's records reflect only the
identity of the Direct Participants to whose accounts such Debentures are
credited, which may or may not be the Beneficial Owners. The Participants will
remain responsible for keeping account of their holdings on behalf of their
customers.
 
     Conveyance of notices and other communications by DTC to Direct
Participants, by Direct Participants to Indirect Participants, and by
Participants to Beneficial Owners will be governed by arrangements among them,
subject to any statutory or regulatory requirements as may be in effect from
time to time.
 
     Neither DTC nor Cede & Co. will consent or vote with respect to Debentures.
Under its usual procedures, DTC would mail an Omnibus Proxy to the Company as
soon as possible after the record date. The Omnibus Proxy assigns Cede & Co.'s
consenting or voting rights to those Direct Participants to whose accounts the
Debentures are credited on the record date (identified in a listing attached to
the Omnibus Proxy).
 
     Principal and interest payments on the Debentures will be made to DTC.
DTC's practice is to credit Direct Participants' accounts on the payable date in
accordance with their respective holdings shown on DTC's records unless DTC has
reason to believe that it will not receive payment on the payable date. Payments
by Participants to Beneficial Owners will be governed by standing instructions
and customary practices, as is the case with securities held for the accounts of
customers in bearer form or registered in "street name," and will be the
responsibility of such Participant and not of DTC or the Company, subject to any
statutory or regulatory requirements as may be in effect from time to time.
Payment of principal and interest to DTC is the responsibility of the Company,
disbursement of such payments to Direct Participants shall be the responsibility
of DTC, and disbursements of such payments to the Beneficial Owners shall be the
responsibility of Participants.
 
     The information in this section concerning DTC and DTC's book-entry system
is based upon information obtained from DTC, and neither the Company, the
Underwriters nor the Trustee takes any responsibility for the accuracy thereof.
 
     Neither the Company, the Trustee nor the Underwriters will have any
responsibility or obligation to Participants, or the persons for whom they act
as nominees, with respect to the accuracy of the records of DTC, its nominee or
any Participant with respect to any ownership interest in the Debentures, or
payments to, or the providing of notice for, Participants or Beneficial Owners.
 
     If the Depository is at any time unwilling or unable to continue as
depository, or has ceased to be qualified to act as such as required by the
Indenture or there shall have occurred and be continuing an Event of Default,
the Company will issue Debentures in definitive form in exchange for the Global
Debentures. In addition, the Company or the Depository may, at any time and in
its sole discretion, determine not to have the Debentures represented by the
Global Debentures and, in such event, the Company will issue Debentures in
definitive form in exchange for the Global Debentures. In either instance, an
owner of the beneficial interest in the Global Debentures will be entitled to
have Debentures equal in principal amount to such beneficial interest registered
in its name and will be entitled to physical delivery of such Debentures in
definitive form. Debentures so issued in definitive form will be issued in
denominations of $1,000 and integral multiples thereof and will be issued in
registered form only, without coupons. (Sections 302 and 305 of the Indenture).
 
                                      S-10
<PAGE>   11
 
                                  UNDERWRITING
 
     Subject to the terms and conditions set forth in an underwriting agreement
(the "Underwriting Agreement") among the Company and Merrill Lynch, Pierce,
Fenner & Smith Incorporated and PaineWebber Incorporated (the "Underwriters"),
the Company has agreed to sell to each of the Underwriters, and each of the
Underwriters has severally agreed to purchase, the respective principal amounts
of Debentures set forth opposite their respective names below. In the
Underwriting Agreement, the several Underwriters have agreed, subject to the
terms and conditions set forth therein, to purchase all of the Debentures if any
are purchased.
 
   
<TABLE>
<CAPTION>
                                                                     PRINCIPAL       PRINCIPAL
                                                                     AMOUNT OF       AMOUNT OF
                                                                      7 1/2%            8%
                                  UNDERWRITER                       DEBENTURES      DEBENTURES
                                                                    -----------     -----------
<S>                                                                 <C>             <C>
Merrill Lynch, Pierce, Fenner & Smith
             Incorporated.........................................  $37,500,000     $37,500,000
PaineWebber Incorporated..........................................   37,500,000      37,500,000
                                                                    -----------     -----------
             Total................................................  $75,000,000     $75,000,000
                                                                    ===========     ===========
</TABLE>
    
 
   
     The Underwriters have advised the Company that they propose to initially
offer the Debentures to the public at the offering prices set forth on the cover
page of this Prospectus Supplement, and to certain dealers at such prices less a
concession not in excess of .4% of the principal amount of the 7 1/2% Debentures
and not in excess of .5% of the principal amount of the 8% Debentures. The
Underwriters may allow, and such dealers may reallow, a discount not in excess
of .25% of the principal amount of the 7 1/2% Debentures and not in excess of
 .25% of the principal amount of the 8% Debentures to other dealers. After the
initial public offering, the public offering prices, concessions and discounts
may be changed.
    
 
     Each series of Debentures is a new issue of securities with no established
trading market. The Company has been advised by the Underwriters that they
intend to make a market in each series of Debentures, but are not obligated to
do so and may discontinue any market making at any time without notice. No
assurance can be given as to the liquidity of the trading market for either
series of Debentures.
 
     The Company has agreed to indemnify the Underwriters against, or contribute
to payments that the Underwriters may be required to make in respect of, certain
liabilities, including liabilities under the Securities Act of 1933, as amended.
 
     Certain of the Underwriters or their affiliates engage in transactions
with, and, from time to time, have performed services for, the Company and its
subsidiaries in the ordinary course of business.
 
                                 LEGAL MATTERS
 
   
     Certain legal matters in connection with the offering of the Debentures
will be passed upon for the Company by Robert M. Johnson, Esq., the Company's
Associate General Counsel, who beneficially owned, either directly or
indirectly, as of June 30, 1996, 1,464 shares of the Company's Common Stock, and
by O'Melveny & Myers LLP and for the Underwriters by Winthrop, Stimson, Putnam &
Roberts.
    
 
                                    EXPERTS
 
     The consolidated financial statements incorporated by reference in this
Prospectus Supplement have been audited by Arthur Andersen LLP, independent
public accountants, as indicated in their report included in the Annual Report
on Form 10-K for the year ended December 31, 1995, and are included herein in
reliance upon the authority of said firm as experts in accounting and auditing
in giving said report.
 
                                      S-11
<PAGE>   12
 
PROSPECTUS
                                  $270,400,000
 
                           SOUTHWEST GAS CORPORATION
            SENIOR DEBT SECURITIES AND SUBORDINATED DEBT SECURITIES
                                PREFERRED STOCK
                               DEPOSITARY SHARES
                                  COMMON STOCK
 
                            SOUTHWEST GAS CAPITAL I
                              PREFERRED SECURITIES
     GUARANTEED TO THE EXTENT SET FORTH HEREIN BY SOUTHWEST GAS CORPORATION
 
    Southwest Gas Corporation (the "Company") may offer from time to time, in
one or more series, its unsecured debt securities (the "Debt Securities"),
consisting of either unsecured Debt Securities which, if issued, will rank on a
parity with all other unsecured and unsubordinated indebtedness of the Company
(the "Senior Debt Securities") or unsecured Debt Securities which, if issued,
will be subordinate and junior in right of payment to certain other indebtedness
of the Company on terms to be determined at the time of the offering (the
"Subordinated Debt Securities"), shares of its Preferred Stock, $50 par value
(the "Preferred Stock") and shares of its Common Stock, $1 par value (the
"Common Stock"). Southwest Gas Capital I, a statutory business trust formed
under the laws of the State of Delaware (the "Trust"), may offer, from time to
time, preferred securities representing undivided beneficial interests in the
assets of the Trust (the "Preferred Securities"). The Debt Securities, the
Preferred Stock, the Common Stock and the Preferred Securities are collectively
referred to herein as the "Securities." Securities will have a maximum aggregate
offering price of $270,400,000 and will be offered on terms to be determined at
the time of offering.
 
    The payment of periodic cash distributions ("distributions") with respect to
the Preferred Securities out of moneys held by the Trust and payments on
liquidation, redemption or otherwise with respect to the Preferred Securities,
will be guaranteed by the Company to the extent described herein (the
"Guarantee"). See "Description of the Guarantee". The Company's obligations
under the Guarantee are subordinate and junior in right of payment to all other
liabilities of the Company and rank pari passu with the most senior preferred
stock, if any, issued from time to time by the Company. Subordinated Debt
Securities may be issued and sold by the Company to the Trust, or a trustee of
the Trust, in connection with the investment of the proceeds from the offering
of Preferred Securities and Common Securities (as defined herein) of the Trust.
The Subordinated Debt Securities purchased by the Trust may be subsequently
distributed pro rata to holders of Preferred Securities and Common Securities in
connection with the dissolution of the Trust upon the occurrence of certain
events as described in an accompanying Prospectus Supplement (as defined below).
 
    In the case of Debt Securities, the specific title, the aggregate principal
amount, the purchase price, the maturity, the rate (or method of calculation)
and time of payment of interest, if any, the right of the Company, if any, to
defer payment of interest on the Debt Securities and the maximum length of such
deferral period, any redemption or sinking fund provisions, any conversion
provisions, any subordination terms, any covenants and any other specific term
of the Debt Securities will be set forth in an accompanying supplement to this
Prospectus (each, a "Prospectus Supplement"). In the case of Preferred Stock,
the specific number of shares, designation, liquidation preference per share,
issuance price, dividend rate (or method of calculation), dividend payment
dates, any redemption or sinking fund provisions, any conversion rights and
other specific terms of the series of Preferred Stock will be set forth in the
accompanying Prospectus Supplement. In addition, the Prospectus Supplement will
describe whether interests in the Preferred Stock will be represented by
depositary shares (the "Depositary Shares") evidenced by depositary receipts
("Depositary Receipts"). In the case of Common Stock, the specific number of
shares and issuance price per share will be set forth in the accompanying
Prospectus Supplement. In the case of Preferred Securities, the designation,
number of securities, liquidation preference per security, purchase price,
distribution rate (or method of calculation thereof), dates on which
distributions shall be payable and dates from which distributions shall accrue,
any voting rights, terms for any conversion or exchange into other securities,
any redemption, exchange or sinking fund provisions, any other rights,
preferences, privileges, limitations or restrictions related to the Preferred
Securities and the terms upon which the proceeds of the sale of the Preferred
Securities shall be used to purchase Subordinated Debt Securities of the Company
will be set forth in the accompanying Prospectus Supplement. The Prospectus
Supplement will also disclose whether the Securities will be listed on a
national securities exchange and if they are not to be listed, the possible
effects thereof on their marketability. If so specified in the accompanying
Prospectus Supplement, Securities may be issued, in whole or in part, in
book-entry form.
 
    Securities may be sold directly, through agents from time to time, through
underwriters and/or dealers or through a combination of such methods. If any
agent of the Company or any underwriter is involved in the sale of the
Securities, the name of such agent or underwriter and any applicable commission
or discount will be set forth in the accompanying Prospectus Supplement. See
"Plan of Distribution."
 
    This Prospectus may not be used to consummate sales of Securities unless
accompanied by a Prospectus Supplement.
                            ------------------------
 
THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
    EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE
       COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON THE
          ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY
             REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.
 
The date of this Prospectus is October 24, 1995
<PAGE>   13
 
                             AVAILABLE INFORMATION
 
     The Company is subject to the informational requirements of the Securities
Exchange Act of 1934 (the "Exchange Act") and, in accordance therewith, files
reports, proxy statements and other information with the Securities and Exchange
Commission (the "Commission"). Such reports, proxy statements and other
information can be inspected and copied at Room 1024 of the offices of the
Commission, Judiciary Plaza, 450 Fifth Street, N.W., Washington, D.C. 20549, and
should be available for inspection and copying at the regional offices of the
Commission located at Seven World Trade Center 13th Floor, New York, New York
10048 and Suite 1400, Northwestern Atrium Center, 500 West Madison Street,
Chicago, Illinois 60661. Copies of such material can be obtained from the
principal offices of the Commission at Judiciary Plaza, 450 Fifth Street, N.W.,
Washington, D.C. 20549 at prescribed rates. Reports, proxy materials and other
information concerning the Company may also be inspected at the offices of the
New York Stock Exchange, 20 Broad Street, New York, New York 10005 and at the
offices of the Pacific Stock Exchange, 301 Pine Street, San Francisco,
California 94104.
 
     No separate financial statements of the Trust have been included herein.
The Company does not consider that such financial statements would be material
to holders of the Preferred Securities because (i) all of the voting securities
of the Trust will be owned directly or indirectly, by the Company, a reporting
company under the Exchange Act, (ii) the Trust has no independent operations but
exists for the sole purpose of issuing securities representing undivided
beneficial interests in the assets of the Trust and investing the proceeds
thereof in Subordinated Debt Securities issued by the Company, and (iii) the
obligations of the Trust under the Trust Securities (as defined herein) will be
fully and unconditionally guaranteed by the Company to the extent that the
Company has made a payment of interest or principal on the Subordinated Debt
Securities. See "Particular Terms of the Subordinated Debt Securities Issued in
Connection with Preferred Securities" and "Description of the Guarantee." The
financial information for the Trust will be included in the consolidated
financial statements of the Company.
 
     This Prospectus does not contain all the information set forth in the
Registration Statement and exhibits thereto which the Company and the Trust have
filed with the Commission under the Securities Act of 1933, and reference is
hereby made to such Registration Statement, including the exhibits thereto.
                            ------------------------
 
                INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE
 
     There are incorporated herein by reference the following documents of the
Company filed with the Commission: (1) Annual Report on Form 10-K for the fiscal
year ended December 31, 1994; (2) Quarterly Reports on Form 10-Q for the
quarters ended March 31, 1995 and June 30, 1995, (3) Current Reports on Form 8-K
dated April 17, 1995 and May 3, 1995; and (4) all documents filed by the Company
pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to
the date of this Prospectus and prior to the termination of the offering of the
Securities.
 
     Any statement contained in a document incorporated or deemed to be
incorporated by reference herein shall be deemed to be modified or superseded
for purposes of this Prospectus to the extent that a statement contained herein,
in a Prospectus Supplement or in any subsequently filed document which is
incorporated by reference herein modifies or supersedes such statements. Any
such statement so modified or superseded shall not be deemed, except as so
modified or superseded, to constitute a part of this Prospectus.
 
     The information relating to the Company contained in this Prospectus
summarizes, is based upon, or refers to, information and financial statements
contained in one or more of the documents incorporated by reference herein;
accordingly, such information contained herein is qualified in its entirety by
reference to such incorporated documents and should be read in conjunction
therewith.
 
     The Company will provide without charge to each person, including any
beneficial holder, to whom a copy of this Prospectus is delivered, upon the
written or oral request of any such person, a copy of any or all the foregoing
documents incorporated by reference herein, including exhibits specifically
incorporated by reference in such documents but excluding all other exhibits to
such documents. Requests should be directed to George C. Biehl, Senior Vice
President and Chief Financial Officer, Southwest Gas Corporation,
 
                                        2
<PAGE>   14
 
5241 Spring Mountain Road, P.O. Box 98510, Las Vegas, Nevada 89193-8510,
telephone number (702) 876-7237.
 
                                  THE COMPANY
 
     The Company, a California corporation, is comprised of two operating
segments: natural gas operations and financial services. The financial services
segment consists of PriMerit Bank, a Federal Savings Bank (the "Bank"), a wholly
owned subsidiary, which operates principally in the thrift industry.
 
     The natural gas operations segment is engaged in the business of
purchasing, transporting, and distributing natural gas in portions of Arizona,
Nevada and California. Its several service areas are geographically as well as
economically diverse. The Company is the largest distributor in Arizona,
distributing and transporting gas in most of southern, central and northwestern
Arizona. The Company is also the largest distributor and transporter of natural
gas in Nevada. The Company also distributes and transports gas in portions of
California, including the Lake Tahoe area and the high desert and mountain areas
in San Bernardino County.
 
     The Company is subject to regulation by the Arizona Corporation Commission,
the Public Service Commission of Nevada (the "PSCN") and the California Public
Utilities Commission (the "CPUC"). The CPUC regulates the issuance of all
securities by the Company, with the exception of short-term borrowings. Certain
of the Company's accounting practices, transmission facilities and rates are
subject to regulation by the Federal Energy Regulatory Commission.
 
     The Bank is a federally chartered stock savings bank conducting business
through branch offices in Nevada. The Bank's deposit accounts are insured to the
maximum extent permitted by law by the Federal Deposit Insurance Corporation
(the "FDIC") through the Savings Association Insurance Fund. The Bank is
regulated by the Office of Thrift Supervision (the "OTS") and the FDIC and is a
member of the Federal Home Loan Bank system.
 
     The Bank's principal business is to attract deposits from the general
public and to make loans secured by real estate and other collateral that enable
borrowers to purchase, refinance, construct or improve such property. Revenues
are derived from interest on real estate loans and debt securities and, to a
lesser extent, from interest on nonmortgage loans, gains on sales of loans and
debt securities, and fees received in connection with loans and deposits. The
Bank's major expense is the interest it pays on savings deposits and borrowings.
 
     The executive offices of the Company are located at 5241 Spring Mountain
Road, P.O. Box 98510, Las Vegas, Nevada 89193-8510, telephone number (702)
876-7237.
 
                                   THE TRUST
 
     The Trust is a statutory business trust formed under Delaware law pursuant
to (i) a declaration of trust (a "Declaration") executed by the Company, as
sponsor for the Trust (the "Sponsor"), and Trustees (as defined herein) of the
Trust and (ii) the filing of a certificate of trust with the Secretary of State
of the State of Delaware on August 17, 1995. The Trust exists for the exclusive
purposes of (i) issuing the Preferred Securities and common securities
representing undivided beneficial interests in the assets of the Trust (the
"Common Securities" and, together with the Preferred Securities, the "Trust
Securities"), (ii) investing the gross proceeds from the sale of the Trust
Securities in the Subordinated Debt Securities and (iii) engaging in only those
other activities necessary or incidental thereto. All of the Common Securities
will be directly or indirectly owned by the Company. The Common Securities will
rank pari passu, and payments will be made thereon pro rata, with the Preferred
Securities, except that, upon an event of default under the Declaration, the
rights of the holders of the Common Securities to payment in respect of
distributions and payments upon liquidation, redemption and otherwise will be
subordinated to the rights of the holders of the Preferred Securities. The
Company will directly or indirectly acquire Common Securities in an aggregate
liquidation amount equal to 3% of the total capital of the Trust. The Trust has
a term of approximately 55 years but may terminate earlier, as provided in the
Declaration.
 
                                        3
<PAGE>   15
 
     The Trust's business and affairs will be conducted by the trustees (the
"Trustees") appointed by the Company as the direct holder of all the Common
Securities. The holder of the Common Securities will be entitled to appoint,
remove or replace any of, or increase or reduce the number of, the Trustees of
the Trust; provided that the number of Trustees may not be reduced to less than
three. The duties and obligations of the Trustees will be governed by the
Declaration. A majority of the Trustees of the Trust will be persons who are
employees or officers of or who are affiliated with the Company (the "Regular
Trustees"). One Trustee of the Trust will be a financial institution that is not
affiliated with the Company, has a specified minimum amount of aggregate
capital, surplus, and undivided profits of not less than $50,000,000 and will
have a principal place of business or reside in the State of Delaware (the
"Delaware Trustee"). The Delaware Trustee will not be a trustee for purposes of
the Trust Indenture Act of 1939, as amended (the "Trust Indenture Act"), and
will not perform the functions of a trustee under such Act. Another financial
institution that is not affiliated with the Company and has a specified minimum
amount of aggregate capital and surplus and undivided profits of not less than
$50,000,000 shall act as property trustee and as indenture trustee and trustee
under the Guarantee, in each case, for the purposes of the Trust Indenture Act
(the "Property Trustee"). The Company will pay all debts and obligations of the
Trust (other than with respect to the Trust Securities) and all fees and
expenses related to the Trust and the offering of the Trust Securities, the
payment of which will be guaranteed by the Company.
 
     The Delaware Trustee for the Trust will be Wilmington Trust Company, 1100
N. Market Street, Wilmington, Delaware 19890. The Property Trustee, indenture
trustee and trustee under the Guarantee will be Harris Trust and Savings Bank,
430 Park Avenue, 14th Floor, New York, New York 10022. The address for the Trust
is c/o Southwest Gas Corporation, the sponsor of the Trust, at the Company's
corporate headquarters located at 5241 Spring Mountain Road, Las Vegas, Nevada
89102, telephone (702) 876-7237.
 
     Harris Trust and Savings Bank and its affiliates may from time to time
maintain lines of credit, act as trustee for senior debt and otherwise have
customary banking relationships with the Company. Neither the Declaration nor
the Indenture for the Subordinated Debt Securities precludes Harris Trust and
Savings Bank or any of its affiliates from enforcing its rights or the rights of
any holders of senior debt for which it acts as trustee as creditors of the
Company unless there is an event of default under the Declaration or the
Indenture for the Subordinated Debt Securities.
 
                                USE OF PROCEEDS
 
     The Trust will use all proceeds received from the sale of the Preferred
Securities to purchase Subordinated Debt Securities from the Company. Except as
otherwise provided in the Prospectus Supplement, the Company intends to use the
proceeds of the sale of the Subordinated Debt Securities to the Trust and the
net proceeds from the sale of other Securities offered hereby to retire
indebtedness and for general corporate purposes, including the acquisition of
property for the construction, completion, extension or improvement of the
Company's pipeline systems and facilities located in and around the communities
it serves.
 
                                        4
<PAGE>   16
 
                      RATIOS OF EARNINGS TO FIXED CHARGES
 
     The following table sets forth the ratios of earnings to fixed charges for
(a) the natural gas operations segment of the Company and (b) the consolidated
gas and financial services operations of the Company (i) without deposit
interest included as a fixed charge and (ii) with deposit interest included as a
fixed charge.
 
<TABLE>
<CAPTION>
                                                                         FOR THE YEARS ENDED
                                                               ----------------------------------------
                                            FOR THE TWELVE
                                             MONTHS ENDED                    DECEMBER 31,
                                               JUNE 30,        ----------------------------------------
                                                 1995          1994     1993     1992     1991     1990
                                            --------------     ----     ----     ----     ----     ----
<S>                                         <C>                <C>      <C>      <C>      <C>      <C>
Ratios of earnings to fixed charges(1):
  Company (natural gas operations
     segment).............................       1.27          1.48     1.25     1.86     1.48     1.84
  Consolidated
     Without deposit interest.............       1.36          1.55     1.32     1.42      (2)     1.45
     With deposit interest................       1.23          1.36     1.18     1.20      (2)     1.24
</TABLE>
 
- ---------------
 
(1) For purposes of computing the ratios of earnings to fixed charges, earnings
    are defined as the sum of pretax income plus fixed charges. Fixed charges
    consist of all interest expense including capitalized interest, one-third of
    rent expense (which approximates the interest component of such expense) and
    amortized debt costs.
 
(2) For the year ended December 31, 1991, consolidated earnings were
    insufficient to cover fixed charges, excluding and including deposit
    interest, by $13.5 million. This was primarily due to the recording of
    additional valuation reserves during 1991 by the Bank.
 
     The following table sets forth the ratios of earnings to combined fixed
charges and preferred and preference stock dividends for (a) the natural gas
segment of the Company and (b) the consolidated gas and financial services
operations of the Company (i) without deposit interest included as a fixed
charge and (ii) with deposit interest included as a fixed charge.
 
<TABLE>
<CAPTION>
                                                                         FOR THE YEARS ENDED
                                                               ----------------------------------------
                                            FOR THE TWELVE
                                             MONTHS ENDED                    DECEMBER 31,
                                               JUNE 30,        ----------------------------------------
                                                 1995          1994     1993     1992     1991     1990
                                            --------------     ----     ----     ----     ----     ----
<S>                                         <C>                <C>      <C>      <C>      <C>      <C>
Ratios of earnings to combined fixed
  charges and preferred and preference
  stock dividends(1)
  Company (natural gas operations
     segment).............................       1.26          1.46     1.23     1.81     1.42     1.75
  Consolidated
     Without deposit interest.............       1.35          1.54     1.30     1.39      (2)     1.43
     With deposit interest................       1.22          1.35     1.17     1.18      (2)     1.22
</TABLE>
 
- ---------------
 
(1) See Note 1 above. Preferred and preference stock dividends have been
    adjusted to represent the pretax earnings necessary to cover such dividend
    requirements.
 
(2) For the year ended December 31, 1991, consolidated earnings were
    insufficient to cover combined fixed charges and preferred and preference
    stock dividends by $14.8 million. This was primarily due to the recording of
    additional valuation reserves during 1991 by the Bank.
 
                         DESCRIPTION OF DEBT SECURITIES
 
     Debt Securities may be issued from time to time in series, either as Senior
Debt Securities or Subordinated Debt Securities, each under an indenture (each,
an "Indenture") between the Company and a bank or trust company selected to act
as trustee as specified in the Prospectus Supplement relating thereto (the
"Trustee"). Each Indenture will be filed as an exhibit to or incorporated by
reference in the Registration Statement of which this Prospectus is a part. As
used under this caption, unless the context otherwise requires, Offered Debt
Securities shall mean the Debt Securities offered by this Prospectus and the
accompanying Prospectus Supplement. The statements under this caption are brief
summaries of certain provisions contained
 
                                        5
<PAGE>   17
 
in the Indenture, do not purport to be complete and are qualified in their
entirety by reference to the applicable Indentures, including the definition
therein of certain terms, a copy of each of which is included or incorporated by
reference as an exhibit to the Registration Statement of which this Prospectus
is a part. Capitalized terms used herein and not defined shall have the meanings
assigned to them in the applicable Indenture. The following sets forth certain
general terms and provisions of the Debt Securities. Additional terms of
Subordinated Debt Securities issued in connection with the Preferred Securities
are set forth under the caption "Particular Terms of Subordinated Debt
Securities Issued in Connection with Preferred Securities." Further terms of the
Offered Debt Securities will be set forth in the Prospectus Supplement.
 
GENERAL
 
     Each Indenture provides for the issuance of Debt Securities in series, and
does not limit the principal amount of Debt Securities which may be issued
thereunder.
 
     The applicable Prospectus Supplement or Prospectus Supplements will
describe the following terms of the series of Offered Debt Securities in respect
of which this Prospectus is being delivered: (a) the title of the Offered Debt
Securities; (b) whether any of the Offered Debt Securities are to be issuable in
bearer form or permanent global form and, if so, the terms and conditions, if
any, upon which interests in such Offered Debt Securities in such bearer form or
global form may be exchanged, in whole or in part, for the Offered Debt
Securities represented thereby; (c) the person to whom any interest on any
Offered Debt Security of the series shall be payable if other than the person in
whose name the Offered Debt Security is registered on the Regular Record Date;
(d) the date or dates on which the Offered Debt Securities will mature; (e) the
rate or rates at which the Offered Debt Securities will bear interest, if any;
(f) the date or dates from which any such interest will accrue, the Interest
Payment Dates on which any such interest on the Offered Debt Securities will be
payable and the Regular Record Date for any interest payable on any Interest
Payment Date; (g) each office or agency where the principal of, premium (if any)
and interest on the Offered Debt Securities will be payable; (h) the period or
periods within which, the events upon the occurrence of which, and the price or
prices at which, the Offered Debt Securities may, pursuant to any optional or
mandatory provisions, be redeemed or purchased, in whole or in part, by the
Company and any terms and conditions relevant thereto; (i) the obligation of the
Company, if any, to redeem or repurchase the Offered Debt Securities at the
option of the Holders; (j) the denominations in which any Offered Debt
Securities will be issuable, if other than denominations of $1,000 and any
integral multiple thereof with respect to Debt Securities, other than
Subordinated Debt Securities issued in connection with Preferred Securities, or
denominations of $25 and any integral multiple thereof with respect to
Subordinated Debt Securities issued in connection with Preferred Securities; (k)
the currency or currencies, including composite currencies, of payment of
principal of and any premium and interest on the Offered Debt Securities, if
other than U. S. Dollars; (l) any index or formula used to determine the amount
of payments of principal of and any premium and interest on the Offered Debt
Securities; (m) if other than the principal amount thereof, the portion of the
principal amount of the Offered Debt Securities of the series which will be
payable upon declaration of the acceleration of the Maturity thereof; (n) any
provisions relating to the conversion or exchange of the Offered Debt Securities
into Common Stock, Preferred Stock or into Debt Securities of another series;
(o) any Events of Default with respect to the Offered Debt Securities, if not
otherwise set forth under "Events of Default"; (p) any material covenants with
respect to the Offered Debt Securities; and (q) any other terms of the Offered
Debt Securities not inconsistent with the provisions of the applicable
Indenture. The applicable Prospectus Supplement will also describe the following
terms of the series of Subordinated Debt Securities offered hereby in respect of
which this Prospectus is being delivered: (a) the rights, if any, to defer
payments of interest on the Subordinated Debt Securities by extending the
interest payment period, and the duration of such extensions, and (b) the
subordination terms of the Subordinated Debt Securities of such series.
 
     Debt Securities may be issued at a discount from their principal amount.
Federal income tax considerations and other special considerations applicable to
any such Original Issue Discount Securities will be described in the applicable
Prospectus Supplement.
 
                                        6
<PAGE>   18
 
     Debt Securities may be issued in bearer form, with or without coupons.
Federal income tax considerations and other special considerations applicable to
bearer securities will be described in the applicable Prospectus Supplement.
 
CONVERSION RIGHTS
 
     The terms, if any, on which Debt Securities of a series may be exchanged
for or converted into shares of Common Stock, Preferred Stock or Debt Securities
of another series will be set forth in the Prospectus Supplement relating
thereto.
 
EXCHANGE, REGISTRATION, TRANSFER AND PAYMENT
 
     Unless otherwise specified in the applicable Prospectus Supplement, payment
of principal, premium, if any, and interest on the Debt Securities will be
payable, and the exchange of and the transfer of Debt Securities will be
registerable, at the office or agency of the Company maintained for such purpose
in New York, New York and at any other office or agency maintained for such
purpose. Unless otherwise indicated in the applicable Prospectus Supplement,
Debt Securities, other than Subordinated Debt Securities issued in connection
with Preferred Securities, will be issued in denominations of $1,000 or integral
multiples thereof. Subordinated Debt Securities issued in connection with
Preferred Securities will be issued in denominations of $25 or integral
multiples thereof. No service charge will be made for any registration of
transfer or exchange of the Debt Securities, but the Company may require payment
of a sum sufficient to cover any tax or other governmental charge imposed in
connection therewith.
 
     All moneys paid by the Company to a Paying Agent for the payment of
principal of and any premium or interest on any Debt Security which remain
unclaimed for two years after such principal, premium or interest has become due
and payable may be repaid to the Company and thereafter the Holder of such Debt
Security may look only to the Company for payment thereof.
 
BOOK-ENTRY DEBT SECURITIES
 
     The Debt Securities of a series may be issued in the form of one or more
Global Securities that will be deposited with a Debt Depositary or its nominee
identified in the applicable Prospectus Supplement. In such a case, one or more
Global Securities will be issued in a denomination or aggregate denominations
equal to the portion of the aggregate principal amount of Outstanding Debt
Securities of the series to be represented by such Global Security or
Securities. Each Global Security will be deposited with such Debt Depositary or
nominee or a custodian therefor and will bear a legend regarding the
restrictions on exchanges and registration of transfer thereof referred to below
and any such other matters as may be provided for pursuant to the applicable
Indenture.
 
     Notwithstanding any provision of the applicable Indenture or any Debt
Security described herein, no Global Security may be transferred to, or
registered or exchanged for Debt Securities registered in the name of, any
Person other than the Debt Depositary for such Global Security or any nominee of
such Debt Depositary, and no such transfer may be registered, unless (a) the
Debt Depositary has notified the Company that it is unwilling or unable to
continue as Debt Depositary for such Global Security or has ceased to be
qualified to act as such as required by the Indenture, (b) the Company executes
and delivers to the Trustee a Company Order that such Global Security shall be
so transferable, registrable and exchangeable, and such transfers shall be
registrable, or (c) there shall exist such circumstances, if any, as may be
described in the applicable Prospectus Supplement. All Debt Securities issued in
exchange for a Global Security or any portion thereof will be registered in such
names as the Debt Depositary may direct.
 
     The specific terms of the depositary arrangement with respect to any
portion of a series of Debt Securities to be represented by a Global Security
will be described in the applicable Prospectus Supplement. The Company expects
that the following provisions will apply to depositary arrangements.
 
     Unless otherwise specified in the applicable Prospectus Supplement, Debt
Securities which are to be represented by a Global Security to be deposited with
or on behalf of a Debt Depositary will be represented by a Global Security
registered in the name of such Debt Depositary or its nominee. Upon the issuance
of such Global Security, and the deposit of such Global Security with or on
behalf of the Debt Depositary for such
 
                                        7
<PAGE>   19
 
Global Security, the Debt Depositary will credit, on its book-entry registration
and transfer system, the respective principal amounts of the Debt Securities
represented by such Global Security to the accounts of institutions that have
accounts with such Debt Depositary or its nominee ("participants"). The accounts
to be credited will be designated by the underwriters or agents of such Debt
Securities or by the Company, if such Debt Securities are offered and sold
directly by the Company. Ownership of beneficial interests in such Global
Security will be limited to participants or Persons that may hold interests
through participants. Ownership of beneficial interests by participants in such
Global Security will be shown on, and the transfer of that ownership interest
will be effected only through, records maintained by the Debt Depositary or its
nominee for such Global Security. Ownership of beneficial interests in such
Global Security by Persons that hold through participants will be shown on, and
the transfer of that ownership interest within such participant will be effected
only through, records maintained by such participant. The laws of some
jurisdictions require that certain purchasers of securities take physical
delivery of such securities in certificated form. The foregoing limitations and
such laws may impair the ability to transfer beneficial interests in such Global
Securities.
 
     So long as the Debt Depositary for a Global Security, or its nominee, is
the registered owner of such Global Security, such Depositary or such nominee,
as the case may be, will be considered the sole owner or Holder of the Debt
Securities represented by such Global Security for all purposes under the
applicable Indenture. Unless otherwise specified in the applicable Prospectus
Supplement, owners of beneficial interests in such Global Security will not be
entitled to have Debt Securities of the series represented by such Global
Security registered in their names, will not receive or be entitled to receive
physical delivery of Debt Securities of such series in certified form and will
not be considered the Holders thereof for any purposes under the applicable
Indenture. Accordingly, each Person owning a beneficial interest in such Global
Security must rely on the procedures of the Debt Depositary and, if such Person
is not a participant, on the procedures of the participant through which such
Person owns its interest, to exercise any rights of a Holder under the
applicable Indenture. The Company understands that under existing industry
practices, if the Company requests any action of Holders or an owner of a
beneficial interest in such Global Security desires to give any notice or take
any action a Holder is entitled to give or take under the applicable Indenture,
the Debt Depositary would authorize the participants to give such notice or take
such action, and participants would authorize beneficial owners owning through
such participants to give such notice or take such action or would otherwise act
upon the instructions of beneficial owners owning through them.
 
     Notwithstanding any other provisions to the contrary in the applicable
Indenture, the rights of the beneficial owners of the Debt Securities to receive
payment of the principal and premium, if any, of and interest on such Debt
Securities, on or after the respective due dates expressed in such Debt
Securities, or to institute suit for the enforcement of any such payment on or
after such respective dates, shall not be impaired or affected without the
consent of the beneficial owners.
 
     Principal of and any premium and interest on a Global Security will be
payable in the manner described in the applicable Prospectus Supplement.
 
CONSOLIDATION, MERGER AND SALE OF ASSETS
 
     The Company, without the consent of any Holders of Outstanding Debt
Securities, may consolidate with or merge into, or transfer or lease its assets
substantially as an entirety to, any Person, and any other Person may
consolidate with or merge into, or transfer or lease its assets substantially as
an entirety to, the Company, provided (a) that the Person (if other than the
Company) formed by such consolidation or into which the Company is merged or
which acquires or leases the assets of the Company substantially as an entirety
is a Person organized and existing under the laws of any United States
jurisdiction and assumes the Company's obligations on the Debt Securities and
under the Indentures, (b) that after giving effect to such transaction no Event
of Default, and no event which, after notice or lapse of time or both, would
become an Event of Default, shall have happened and be continuing, and (c) that
certain other conditions are met.
 
COVENANTS OF THE COMPANY
 
     The applicable Prospectus Supplement will describe any material covenants
in respect of a series of Offered Debt Securities. Other than the covenants of
the Company included in the Indentures as described
 
                                        8
<PAGE>   20
 
above or as described in the applicable Prospectus Supplement, there are no
covenants or provisions in the Offered Debt Securities or the Indentures that
limit or restrict the Company's business or operations, the pledging of the
Company's assets or the incurrence of indebtedness by the Company or that may
afford Holders protection in the event of a highly leveraged transaction or
leveraged buyout involving the Company.
 
EVENTS OF DEFAULT
 
     Unless otherwise specified in the applicable Prospectus Supplement, the
following are Events of Default under the Indentures with respect to Debt
Securities of any series: (a) failure to pay principal of or premium, if any, on
any Debt Security of that series when due; provided, however, that a valid
extension of the maturity of Subordinated Debt Securities shall not constitute a
default for this purpose; (b) failure to pay any interest on any Debt Security
of that series when due, continued for 30 days; provided, however, that a valid
extension of the interest payment provided by the Company for the Subordinated
Debt Securities shall not constitute a default in the payment of interest for
this purpose, and provided further that, if Subordinated Debt Securities are
issued to the Trust or a Trustee of the Trust in connection with the issuance of
Trust Securities by the Trust, such 30-day period will be replaced by a ten day
period; (c) failure to make any sinking fund payment, when due, in respect of
any Debt Security of that series; (d) failure to perform any other covenant of
the Company in the Indenture (other than a covenant included in the Indenture
solely for the benefit of a series of Debt Securities other than that series),
continued for 60 days after written notice by the Trustee or Holders of at least
25% in principal amount of the Outstanding Debt Securities of that series as
provided in the Indenture; (e) a default under any evidence of indebtedness for
money borrowed by the Company (including a default with respect to Debt
Securities of any other series) in an individual principal amount outstanding of
at least $15,000,000 or under any instrument under which there may be issued or
by which there may be secured or evidenced any indebtedness for money borrowed
by the Company (including the Indentures) in an individual principal amount
outstanding of at least $15,000,000, whether such indebtedness exists as of the
date of the applicable Indenture or is thereafter created, which default shall
constitute a failure to pay any portion of the principal of such indebtedness
when due and payable after the expiration of any applicable grace period with
respect thereto or which default results in the acceleration of such
indebtedness without such indebtedness having been discharged, or such
acceleration having been rescinded or annulled, within 10 Business Days after
written notice to the Company by the Trustee or by the Holders of at least 25%
in principal amount of the Outstanding Debt Securities of such series as
provided in the Indenture; (f) certain events of bankruptcy, insolvency or
reorganization of the Company; (g) the voluntary or involuntary dissolution of
the Trust pursuant to which (or of a Trustee of the Trust to which) Subordinated
Debt Securities were issued in connection with the issuance of Trust Securities
by the Trust, except in connection with the distribution of Subordinated Debt
Securities to the holders of Trust Securities in liquidation of the Trust, the
redemption of all of the Trust Securities, or certain mergers, consolidations or
amalgamations, each as permitted by the Declaration; and (h) any other Event of
Default provided with respect to Debt Securities of that series. If an Event of
Default with respect to Outstanding Debt Securities of any series shall occur
and be continuing, either the Trustee or the Holders of at least 25% in
principal amount of the Outstanding Debt Securities of that series by notice as
provided in the applicable Indenture may declare the principal amount (or, if
the Debt Securities of that series are Original Issue Discount Securities, such
portion of the principal amount as may be specified in the terms of that series)
of all Debt Securities of that series to be due and payable immediately.
However, at any time after a declaration of acceleration with respect to Debt
Securities of any series has been made, but before a judgment or decree based on
such acceleration has been obtained, the Holders of a majority in principal
amount of the Outstanding Debt Securities of that series may, under certain
circumstances, rescind and annul such acceleration. For information as to waiver
of defaults, see "Modification and Waiver" below.
 
     Each Indenture provides that, subject to the duty of the Trustee during an
Event of Default to act with the required standard of care, the Trustee will be
under no obligation to exercise any of its rights or powers under the Indenture
at the request or direction of any of the Holders, unless such Holders shall
have offered to the Trustee reasonable security or indemnity. Subject to certain
provisions, including those requiring security
 
                                        9
<PAGE>   21
 
or indemnification of the Trustee, the Holders of a majority in principal amount
of the Outstanding Debt Securities of any series will have the right to direct
the time, method and place of conducting any proceeding for any remedy available
to the Trustee, or exercising any trust or power conferred on the Trustee, with
respect to the Debt Securities of that series.
 
     The Company will be required to furnish to the Trustee under each Indenture
annually a statement as to the performance by the Company of its obligations
under the Indenture and as to any default in such performance.
 
MODIFICATION AND WAIVER
 
     Modifications and amendments of the Indenture may be made by the Company
and the Trustee with the consent of the Holders of not less than a majority in
principal amount of the Outstanding Debt Securities of each series affected
thereby; provided, however, that no such modification or amendment may, without
the consent of the Holder of each Outstanding Debt Security affected thereby;
(a) change the Stated Maturity of the principal of, or any installment of
principal of, or interest on, any Debt Security; (b) reduce the principal amount
of, the rate of interest on, or the premium, if any, payable upon the redemption
of, any Debt Security; (c) reduce the amount of principal of an Original Issue
Discount Security payable upon acceleration of the Maturity thereof; (d) change
the currency of payment of principal of, or premium, if any, or interest on any
Debt Security; (e) impair the right to institute suit for the enforcement of any
payment on or with respect to any Debt Security on or after the Stated Maturity
or Redemption Date thereof; or (f) reduce the percentage in principal amount of
Outstanding Debt Securities of any series, the consent of the Holders of which
is required for modification or amendment of the applicable Indenture or for
waiver of compliance with certain provisions of the applicable Indenture or for
waiver of certain defaults.
 
     The Holders of at least a majority in principal amount of the Outstanding
Debt Securities of any series may on behalf of the Holders of all Debt
Securities of that series waive, insofar as that series is concerned, compliance
by the Company with certain covenants of the Indenture. The applicable
Prospectus Supplement will describe the terms of any such covenants. The Holders
of not less than a majority in principal amount of the Outstanding Debt
Securities of any series may, on behalf of the Holders of all Debt Securities of
that series, waive any past default under the applicable Indenture with respect
to that series, except a default in the payment of the principal of, or premium,
if any, or interest on, any Debt Security of that series or in respect of a
provision which under such Indenture cannot be modified or amended without the
consent of the Holder of each Outstanding Debt Security of that series affected.
 
DEFEASANCE
 
     Unless otherwise specified in the applicable Prospectus Supplement with
respect to the Debt Securities of a series, other than Subordinated Debt
Securities issued in connection with Preferred Securities, the Company, at its
option, (i) will be discharged from any and all obligations in respect of the
Debt Securities of such series (except for certain obligations to register the
transfer or exchange of Debt Securities of such series, to replace destroyed,
stolen, lost or mutilated Debt Securities of such series, and to maintain Paying
Agents and hold moneys for payment in trust) or (ii) need not comply with
certain covenants specified in the applicable Prospectus Supplement with respect
to the Debt Securities of that series, and the occurrence of an event described
in clause (d) under "Events of Default" above with respect to any defeased
covenant and clauses (e) and (g) of the "Events of Default" above shall no
longer be an Event of Default if, in either case, the Company deposits with the
Trustee, in trust, money or U.S. Government Obligations that through the payment
of interest thereon and principal thereof in accordance with their terms will
provide money in an amount sufficient to pay all the principal of (and premium,
if any) and any interest on the Debt Securities of such series on the dates such
payments are due (which may include one or more redemption dates designated by
the Company) in accordance with the terms of such Debt Securities. Such a trust
may only be established if, among other things, (a) no Event of Default or event
which with the giving of notice or lapse of time, or both, would become an Event
of Default under the applicable Indenture shall have occurred and be continuing
on the date of such deposit, (b) no Event of Default described under clause (f)
under "Events of Default" above or event which with the giving of notice or
lapse of time, or both, would become an Event of Default described under such
clause (f) shall have occurred and be continuing at any time during the period
ending on the 91st day following such date of deposit, and (c) the Company shall
have delivered an Opinion of Counsel
 
                                       10
<PAGE>   22
 
to the effect that the Holders of the Debt Securities will not recognize gain or
loss for Federal income tax purposes as a result of such deposit or defeasance
and will be subject to Federal income tax in the same manner as if such
defeasance had not occurred. In the event the Company omits to comply with its
remaining obligations under the applicable Indenture after a defeasance of the
Indenture with respect to the Debt Securities of any series as described under
clause (ii) above and the Debt Securities of such series are declared due and
payable because of the occurrence of any undefeased Event of Default, the amount
of money and U.S. Government Obligations on deposit with the Trustee may be
insufficient to pay amounts due on the Debt Securities of such series at the
time of the acceleration resulting from such Event of Default. However, the
Company will remain liable in respect of such payments.
 
GOVERNING LAW
 
     Each Indenture and the Debt Securities will be governed by, and construed
in accordance with, the laws of the State of New York.
 
REGARDING THE TRUSTEE
 
     Each Indenture contains certain limitations on the right of the Trustee,
should it become a creditor of the Company, to obtain payment of claims in
certain cases, or to realize for its own account on certain property received in
respect of any such claim as security or otherwise. The Trustee will be
permitted to engage in certain other transactions; however, if it acquires any
conflicting interest and there is a default under the Debt Securities, it must
eliminate such conflict or resign.
 
                PARTICULAR TERMS OF SUBORDINATED DEBT SECURITIES
                 ISSUED IN CONNECTION WITH PREFERRED SECURITIES
 
     The statements under this caption are brief summaries of certain provisions
of the Subordinated Debt Securities Indenture applicable to Subordinated Debt
Securities issued in connection with Preferred Securities, do not purport to be
complete and are qualified in their entirety by reference to the Subordinated
Debt Securities Indenture.
 
     In the event Subordinated Debt Securities are issued to the Trust or a
Trustee of the Trust in connection with the issuance of Trust Securities by the
Trust, such Subordinated Debt Securities subsequently may be distributed pro
rata to the holders of the Trust Securities in connection with the dissolution
of the Trust upon the occurrence of certain events described in the applicable
Prospectus Supplement relating to the Trust Securities. Only one series of
Subordinated Debt Securities will be issued to the Trust or a Trustee of the
Trust in connection with the issuance of Trust Securities by the Trust.
 
     If Subordinated Debt Securities are issued to the Trust or a Trustee of the
Trust in connection with the issuance of Trust Securities and (i) there shall
have occurred any event that would constitute an Event of Default, (ii) the
Company shall be in default with respect to its payment of any obligations under
the Guarantee or Common Securities Guarantee, or (iii) the Company shall have
given notice of its election to defer payments of interest on such Subordinated
Debt Securities by extending the interest payment period as provided in the
Subordinated Debt Securities Indenture and such period, or any extension
thereof, shall be continuing, then (a) the Company shall not declare or pay
dividends on, or make a distribution with respect to or redeem, purchase or
acquire, or make a liquidation payment with respect to, any of its capital stock
and (b) the Company shall not make any payment of interest, principal or
premium, if any, on or repay, repurchase or redeem any debt securities issued by
the Company which rank pari passu with or junior to such Subordinated Debt
Securities; provided, however, that, restriction (a) above does not apply to any
stock dividends paid by the Company where the dividend stock is the same stock
as that on which the dividend is being paid.
 
     In the event Subordinated Debt Securities are issued to the Trust or a
Trustee of the Trust in connection with the issuance of Trust Securities, for so
long as the Trust Securities remain outstanding, the Company will covenant (i)
to directly or indirectly maintain 100% ownership of the Common Securities;
provided, however, that any permitted successor of the Company under the
Subordinated Debt Securities Indenture may succeed
 
                                       11
<PAGE>   23
 
to the Company's ownership of the Common Securities and (ii) to use its
reasonable efforts to cause the Trust (a) to remain a statutory business trust,
except in connection with the distribution of Subordinated Debt Securities to
the holders of Trust Securities in liquidation of the Trust, the redemption of
all of the Trust Securities, or certain mergers, consolidations or
amalgamations, each as permitted by the Declaration, and (b) to otherwise
continue to be classified as a grantor trust for United States federal income
tax purposes.
 
                    DESCRIPTION OF THE PREFERRED SECURITIES
 
     The Trust may issue, from time to time, only one series of Preferred
Securities having terms described in the Prospectus Supplement relating thereto.
The Declaration authorizes the Regular Trustees of the Trust to issue on behalf
of the Trust one series of Preferred Securities. The Declaration will be
qualified as an indenture under the Trust Indenture Act.
 
     The Preferred Securities will have such terms, including distribution,
redemption, voting and liquidation rights and such other preferred, deferred or
other special rights or such restrictions as shall be set forth in the
Declaration or made part of the Declaration by the Trust Indenture Act.
Reference is made to the applicable Prospectus Supplement relating to the
Preferred Securities for specific terms, including (i) the distinctive
designation of the Preferred Securities, (ii) the number of Preferred Securities
and the date or dates upon which distributions shall be payable (provided,
however, that, distributions on the Preferred Securities shall be payable on a
quarterly basis to holders of the Preferred Securities as of a record date in
each quarter during which the Preferred Securities are outstanding), (iii)
whether distributions on Preferred Securities issued by the Trust shall be
cumulative, and, in the case of Preferred Securities having such cumulative
distribution rights, the date or dates or method of determining the date or
dates from which distributions on Preferred Securities shall be cumulative, (iv)
the amount or amounts which shall be paid out of the assets of the Trust to the
holders of Preferred Securities upon voluntary or involuntary dissolution,
winding-up or termination of the Trust, (v) the obligation, if any, of the Trust
to purchase or redeem Preferred Securities and the price or prices at which, the
period or periods within which and the terms and conditions upon which the
Preferred Securities shall be purchased or redeemed, in whole or in part,
pursuant to such obligation, (vi) the voting rights, if any, of Preferred
Securities in addition to those required by law, including the number of votes
per Preferred Security and any requirement for the approval by the holders of
Preferred Securities, as a condition to specified action or amendments to the
Declaration, and (vii) any other relevant rights, preferences, privileges,
limitations or restrictions on Preferred Securities consistent with the
Declaration and applicable law.
 
     All Preferred Securities offered hereby will be guaranteed by the Company
to the extent set forth below under "Description of the Guarantee". Certain
United States federal income tax considerations applicable to any offering of
Preferred Securities will be described in the Prospectus Supplement relating
thereto.
 
     In connection with the issuance of Preferred Securities, the Trust will
issue Common Securities having such terms including distribution, redemption,
voting and liquidation rights or such restrictions as shall be set forth
therein. The terms of the Common Securities will be substantially identical to
the terms of the Preferred Securities and the Common Securities, will rank pari
passu, and payments will be made thereon pro rata with the Preferred Securities
except that, upon an event of default under the Declaration, the rights of the
holders of the Common Securities to payment in respect of distributions and
payments upon liquidation, redemption and otherwise will be subordinated to the
rights of the holders of the Preferred Securities. Except in certain limited
circumstances, the Common Securities will also carry the right to vote and to
appoint, remove or replace any of the Trustees of the Trust. All of the Common
Securities will be directly or indirectly owned by the Company.
 
                                       12
<PAGE>   24
 
                          DESCRIPTION OF THE GUARANTEE
 
     Set forth below is a summary of information concerning the Guarantee that
will be executed and delivered by the Company for the benefit of the holders,
from time to time, of Preferred Securities. The Bank will have no obligation
under the Guarantee. The Guarantee will be qualified as an indenture under the
Trust Indenture Act. Harris Trust and Savings Bank will act as indenture trustee
under the Guarantee (the "Guarantee Trustee"). The terms of the Guarantee will
be those set forth in the Guarantee and those made part of the Guarantee by the
Trust Indenture Act. This summary does not purport to be complete and is subject
in all respects to the provisions of, and is qualified in its entirety by
reference to, the form of Guarantee, which is filed as an exhibit to the
Registration Statement of which this Prospectus forms a part, and the Trust
Indenture Act. The Guarantee will be held by the Guarantee Trustee for the
benefit of the holders of the Preferred Securities.
 
GENERAL
 
     Pursuant to the Guarantee, the Company will irrevocably and unconditionally
agree, to the extent set forth herein, to pay in full to the holders of the
Preferred Securities, the Guarantee Payments (as defined herein) (except to the
extent paid by the Trust), as and when due, regardless of any defense, right of
set-off or counterclaim which the Trust may have or assert. The following
payments with respect to Preferred Securities (the "Guarantee Payments"), to the
extent not paid by the Trust will be subject to the Guarantee (without
duplication): (i) any accrued and unpaid distributions that are required to be
paid on the Preferred Securities, to the extent the Company has made a payment
of interest or principal on the Subordinated Debt Securities, (ii) the
redemption price, including all accrued and unpaid distributions thereon,
including interest thereon to the date of redemption (the "Redemption Price"),
to the extent the Company has made a payment of interest or principal on the
Subordinated Debt Securities with respect to any Preferred Securities called for
redemption by the Trust and (iii) upon a voluntary or involuntary dissolution,
winding-up or termination of the Trust (other than in connection with the
distribution of Subordinated Debt Securities to the holders of Preferred
Securities or the redemption of all the Preferred Securities upon the redemption
or maturity of the Subordinated Debt Securities) the lesser of (a) the aggregate
of the liquidation amount and all accrued and unpaid distributions on the
Preferred Securities to the date of payment to the extent the Trust has funds
available therefor or (b) the amount of assets of the Trust remaining available
for distribution to holders of the Preferred Securities in liquidation of the
Trust. The Company's obligation to make a Guarantee Payment may be satisfied by
direct payment of the required amounts by the Company to the holders of
Preferred Securities or by causing the Trust to pay such amounts to such
holders.
 
     The Guarantee will be a full and unconditional guarantee on a subordinated
basis with respect to the Preferred Securities from the time of issuance, but
will not apply to any payment of distributions, except to the extent the Trust
shall have funds available therefor as a result of payments of interest or
principal on the Subordinated Debt Securities by the Company. If the Company
does not make interest payments on the Subordinated Debt Securities purchased by
the Trust, the Trust will not pay distributions on the Preferred Securities and
will not have funds available therefor. See "Particular Terms of Subordinated
Debt Securities Issued in Connection with Preferred Securities."
 
     The obligations of the Company under the Declaration, the Guarantee, the
Indenture with respect to the Subordinated Debt Securities issued in connection
with the Preferred Securities and the Subordinated Debt Securities issued in
connection with the Preferred Securities collectively provide a full and
unconditional guarantee on a subordinated basis by the Company of payments due
on the Preferred Securities to the extent the Trust has funds available therefor
as a result of payments of interest or principal on the Subordinated Debt
Securities by the Company.
 
     The Company has also agreed to irrevocably and unconditionally guarantee
the obligations of the Trust with respect to the Common Securities (the "Common
Securities Guarantee") to the same extent as the Guarantee, except that, upon an
event of default under the Subordinated Debt Securities Indenture, holders of
Preferred Securities under the Guarantee will have priority over holders of
Common Securities under the
 
                                       13
<PAGE>   25
 
Common Securities Guarantee with respect to distributions and payments on
liquidation, redemption or otherwise.
 
CERTAIN COVENANTS OF THE COMPANY
 
     In the Guarantee, the Company will covenant that, so long as any Preferred
Securities issued by the Trust remain outstanding, if there shall have occurred
any event that would constitute an event of default under the Guarantee or the
Declaration, then (a) the Company shall not declare or pay any dividend on, or
make any distribution with respect to, or redeem, purchase, acquire or make a
liquidation payment with respect to, any of its capital stock and (b) shall not
make any payment of interest, principal or premium, if any, on or repay,
repurchase or redeem any debt securities issued by the Company which rank pari
passu with or junior to such Subordinated Debt Securities. However, the
Guarantee will except from the foregoing any stock dividends paid by the
Company, where the dividend stock is the same stock as that on which the
dividend is being paid.
 
MODIFICATIONS OF THE GUARANTEE; ASSIGNMENT
 
     Except with respect to any changes that do not adversely affect the rights
of holders of Preferred Securities (in which case no vote will be required), the
Guarantee may be amended only with the prior approval of the holders of not less
than 66 2/3% in liquidation amount of the Preferred Securities then outstanding.
The manner of obtaining any such approval of holders of the Preferred Securities
will be set forth in an accompanying Prospectus Supplement. All guarantees and
agreements contained in the Guarantee shall bind the successors, assigns,
receivers, trustees and representatives of the Company and shall inure to the
benefit of the holders of the Preferred Securities then outstanding.
 
EVENTS OF DEFAULT
 
     An event of default under the Guarantee will occur upon the failure of the
Company to make any of the payments required by the Guarantee or to perform its
other obligations thereunder. The holders of a majority in liquidation amount of
the 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 the Guarantee or to direct the exercise of any trust or power
conferred upon the Guarantee Trustee under the Guarantee.
 
     If the Guarantee Trustee fails to enforce the Guarantee, any holder of
Preferred Securities may institute a legal proceeding directly against the
Company to enforce the Guarantee Trustee's rights under the Guarantee without
first instituting a legal proceeding against the Trust, the Guarantee Trustee or
any other person or entity.
 
     The Company will be required to provide annually to the Guarantee Trustee a
statement as to the performance by the Company of certain of its obligations
under the Guarantee and as to any default in such performance.
 
     The Company is required to file annually with the Guarantee Trustee an
officer's certificate as to the Company's compliance with all conditions under
the Guarantee.
 
INFORMATION CONCERNING THE GUARANTEE TRUSTEE
 
     The Guarantee Trustee, prior to the occurrence of a default, undertakes to
perform only such duties as are specifically set forth in the Guarantee and,
after default with respect to the Guarantee, shall exercise the same degree of
care as a prudent individual would exercise in the conduct of its own affairs.
Subject to such provision, the Guarantee Trustee is under no obligation to
exercise any of the powers vested in it by the Guarantee at the request of any
holder of Preferred Securities unless it is offered reasonable indemnity against
the costs, expenses and liabilities that might be incurred thereby.
 
TERMINATION OF THE GUARANTEE
 
     The Guarantee will terminate as to the Preferred Securities upon full
payment of the Redemption Price of all Preferred Securities, upon distribution
of the Subordinated Debt Securities held by the Trust to the
 
                                       14
<PAGE>   26
 
holders of the Preferred Securities or upon full payment of the amounts payable
in accordance with the Declaration upon liquidation of the Trust. The Guarantee
will continue to be effective or will be reinstated, as the case may be, if at
any time any holder of Preferred Securities must restore payment of any sums
paid under the Preferred Securities or the Guarantee.
 
STATUS OF THE GUARANTEE
 
     The Guarantee will constitute an unsecured obligation of the Company and
will rank (i) subordinate and junior in right of payment to all other
liabilities of the Company (other than the Common Securities Guarantee or any
guarantee now or hereafter entered into by the Company in respect of any
preferred or preference stock of any Affiliate of the Company), (ii) pari passu
with the most senior preferred or preference stock now or hereafter issued by
the Company and with any guarantee now or hereafter entered into by the Company
in respect of any preferred or preference stock of any Affiliate of the Company
and (iii) senior to the Company's Common Stock. The terms of the Preferred
Securities provide that each holder of Preferred Securities by acceptance
thereof agrees to the subordination provisions and other terms of the Guarantee.
 
     The Guarantee will constitute a guarantee of payment and not of collection
(that is, the guaranteed party may institute a legal proceeding directly against
the guarantor to enforce its rights under the Guarantee without instituting a
legal proceeding against any other person or entity).
 
GOVERNING LAW
 
     The Guarantee will be governed by and construed in accordance with the
internal laws of the State of New York.
 
                         DESCRIPTION OF PREFERRED STOCK
 
     The following description of the terms of the Preferred Stock sets forth
certain general terms and provisions of the Preferred Stock to which any
Prospectus Supplement may relate. Certain other terms of any series of the
Preferred Stock offered by any Prospectus Supplement will be described in such
Prospectus Supplement. The description of certain provisions of the Preferred
Stock set forth below and in any Prospectus Supplement does not purport to be
complete and is subject to and qualified in its entirety by reference to the
Company's Restated Articles of Incorporation (the "Articles of Incorporation"),
and the certificate of determination (a "Certificate of Determination") relating
to each series of the Preferred Stock which will be filed with the Commission
and incorporated by reference as an exhibit to the Registration Statement of
which this Prospectus is a part at or prior to the time of the issuance of such
series of the Preferred Stock.
 
AUTHORIZED CAPITAL STOCK
 
     The authorized capital stock of the Company consists of 30,000,000 shares
of Common Stock, $1 par value, 200,000 shares of preferred stock, $50 par value
("preferred stock of the Company," which term, as used herein, includes the
Preferred Stock offered hereby), 500,000 shares of cumulative preferred stock,
$100 par value ("Cumulative Preferred Stock"), and 2,000,000 shares of
preference stock, $20 par value (the "Preference Stock"). As of June 30, 1995
there were outstanding 23,898,709 shares of Common Stock and 40,000 shares of
Cumulative Preferred Stock. No shares of preferred stock of the Company or
Preference Stock of the Company were outstanding on this date.
 
     The Company is required to redeem 8,000 shares annually through 1999 of the
Cumulative Preferred Stock at par value plus accrued dividends. All outstanding
shares of Cumulative Preferred Stock are redeemable at the option of the Company
at any time upon 30 days' notice at par value plus accrued dividends and a
premium equal to the dividend rate in the first year commencing December 1, 1979
and declining ratably each year thereafter to par value. In addition, the
Company may redeem up to 8,000 shares of Cumulative Preferred Stock (but not
more than 45,000 shares in the aggregate) at par value plus accrued dividends on
any mandatory redemption date without payment of a premium. The dividend rate on
the Cumulative Preferred Stock is 9.5% and is cumulative.
 
                                       15
<PAGE>   27
 
     The Articles of Incorporation provide that in the event of involuntary
liquidation, (a) before distributions may be made to holders of any other class
of Junior Stock (as hereinafter defined), holders of Cumulative Preferred Stock
are entitled to payment in full at par value, together with accrued dividends.
 
     The holders of shares of the Cumulative Preferred Stock are not entitled to
notice of any meetings of shareholders or to vote upon the election of directors
or upon any question affecting the management or affairs of the Company, except
to the extent otherwise provided by law or the Certificate of Determination for
the Cumulative Preferred Stock. The Certificate of Determination for the
Cumulative Preferred Stock provides that the holders of all shares of Cumulative
Preferred Stock, voting as a class, are entitled to elect two directors to the
Board of Directors of the Company whenever four quarterly dividends upon any
shares of Cumulative Preferred Stock are in arrears or any mandatory redemption
payment is one year in arrears, until all dividends in default and mandatory
redemption payments have been made. In addition, an affirmative vote of the
holders of all shares of Cumulative Preferred Stock outstanding is required for
the authorization or creation (or increase in the authorized amount) of any
class of stock ranking senior to the Cumulative Preferred Stock. It is, however,
permissible to issue up to 200,000 shares of preferred stock of the Company
senior to the Cumulative Preferred Stock. The affirmative vote of 66 2/3% of the
outstanding shares of Cumulative Preferred Stock is also required in order (a)
to amend the Articles of Incorporation in certain respects that would adversely
affect the rights of the holders of Cumulative Preferred Stock, (b) to increase
the amount of Cumulative Preferred Stock authorized by the Articles of
Incorporation or the authorization or creation of any class of stock ranking on
a parity with the Cumulative Preferred Stock, (c) for the Company to sell, lease
or convey substantially all of the business of the Company, the parting of
control thereof or the merger or consolidation of the Company into another
corporation in which the Company is not the surviving corporation, or (d) to
issue or reissue any shares of Cumulative Preferred Stock ranking on a parity
with the Cumulative Preferred Stock unless certain financial tests are met.
 
ISSUANCE OF PREFERRED STOCK
 
     Under the Articles of Incorporation, the Board of Directors of the Company
is authorized without further shareholder action to provide for the issuance of
up to 200,000 shares of preferred stock of the Company in preference to the
holders of Cumulative Preferred Stock, Preference Stock and Common Stock (the
Common Stock, Cumulative Preferred Stock and Preference Stock being herein
referred to as "Junior Stock"), in one or more series, with such dividend
rights, dividend rate, conversion rights, voting rights, rights and time of
redemption (including sinking fund provisions), redemption price or prices,
liquidation preferences and designation, as shall be stated in the resolution or
resolutions providing for the issue of a series of such preferred stock of the
Company adopted, at any time or from time to time, by the Board of Directors of
the Company. The Board of Directors may also increase or decrease (but not below
the number of shares of such series then outstanding) the number of shares of
any such series subsequent to the issue of that series.
 
     As described under "Description of Depositary Shares," the Company may, at
its option, elect to offer Depositary Shares evidenced by depositary receipts
(the "Depositary Receipts"), each representing a fraction (to be specified in
the Prospectus Supplement relating to the particular series of the Preferred
Stock) of a share of the particular series of the Preferred Stock issued and
deposited with a depositary, in lieu of offering full shares of such series of
the Preferred Stock.
 
     The Preferred Stock shall have the dividend, liquidation, redemption and
voting rights set forth below unless otherwise provided in a Prospectus
Supplement relating to a particular series of the Preferred Stock. Reference is
made to the Prospectus Supplement relating to the particular series of the
Preferred Stock offered thereby for specific terms, including: (a) the
designation of such Preferred Stock and the number of shares offered; (b) the
amount of liquidation preference per share; (c) the initial public offering
price at which such Preferred Stock will be issued; (d) the dividend rate (or
method of calculation), the dates on which dividends shall be payable and the
dates from which dividends shall commence to cumulate, if any; (e) any
redemption or sinking fund provisions; (f) any conversion rights; (g) whether
the Company has elected to offer Depositary Shares as described below under
"Description of Depositary Shares;" and (h) any additional voting, dividend,
liquidation, redemption, sinking fund and other rights, preferences, privileges,
limitations and restrictions.
 
                                       16
<PAGE>   28
 
     The Preferred Stock will, when issued, be fully paid and nonassessable and
will have no preemptive rights. The rights of the holders of each series of the
Preferred Stock to receive dividends and distributions of assets will be
subordinate to those of the Company's general creditors, but superior to the
rights of holders of Junior Stock. See "Description of Common Stock" for a
description of certain provisions of State and federal law and the Articles of
Incorporation and Bylaws of the Company which may affect holders of Preferred
Stock.
 
DIVIDEND RIGHTS
 
     Holders of the Preferred Stock of each series will be entitled to receive,
when, as and if declared by the Board of Directors of the Company, out of funds
of the Company legally available therefor, cash dividends on such dates and at
such rates as are set forth in, or as are determined by the method described in,
the Prospectus Supplement relating to such series of the Preferred Stock. Such
rate may be fixed or variable or both. Each such dividend will be payable to the
holders of record as they appear on the stock books of the Company (or, if
applicable, the records of the Depositary (as hereinafter defined) referred to
under "Description of Depositary Shares") on such record dates, fixed by the
Board of Directors of the Company, as specified in the Prospectus Supplement
relating to such series of Preferred Stock.
 
     Such dividends may be cumulative or noncumulative, as provided in the
Prospectus Supplement relating to such series of Preferred Stock. If the Board
of Directors of the Company fails to declare a dividend payable on a dividend
payment date on any series of Preferred Stock for which dividends are
noncumulative, then the right to receive a dividend in respect of the dividend
period ending on such dividend payment date will be lost, and the Company will
have no obligation to pay the dividend accrued for such period, whether or not
dividends on such series are declared payable on any future dividend payment
dates. Dividends on the shares of each series of Preferred Stock for which
dividends are cumulative will accrue from the date on which the Company
initially issues shares of such series.
 
     Unless otherwise specified in the applicable Prospectus Supplement, so long
as the shares of any series of the Preferred Stock are outstanding, unless (a)
full dividends (including if such Preferred Stock is cumulative, dividends for
prior dividend periods) have been paid or declared and set apart for payment on
all outstanding shares of the Preferred Stock of such series and all other
classes and series of preferred stock of the Company (other than Junior Stock)
and (b) the Company is not in default or in arrears with respect to the
mandatory or optional redemption or mandatory repurchase or other mandatory
retirement of, or with respect to any sinking or other analogous fund for, any
shares of Preferred Stock of such series or any shares of any other preferred
stock of the Company of any class or series (other than Junior Stock), the
Company may not declare any dividends on any shares of Common Stock of the
Company or any other stock of the Company ranking as to dividends or
distributions of assets junior to such series of Preferred Stock, or make any
payment on account of, or set apart money for, the purchase, redemption or other
retirement of, or for a sinking or other analogous fund for, any shares of
Junior Stock or make any distribution in respect thereof, whether in cash or
property or in obligations or stock of the Company, other than Junior Stock
which is neither convertible into, nor exchangeable or exercisable for, any
securities of the Company other than Junior Stock.
 
LIQUIDATION PREFERENCES
 
     Unless otherwise specified in the applicable Prospectus Supplement, in the
event of any liquidation, dissolution or winding up of the Company, whether
voluntary or involuntary, the holders of each series of the Preferred Stock will
be entitled to receive out of the assets of the Company available for
distribution to shareholders, before any distribution of assets is made to the
holders of Junior Stock, the amount set forth in the Prospectus Supplement
relating to such series of the Preferred Stock. If, upon any voluntary or
involuntary liquidation, dissolution or winding up of the Company, the amounts
payable with respect to the Preferred Stock of any series and any other shares
of preferred stock of the Company (including any other series of the Preferred
Stock) ranking as to any such distribution on a parity with such series of the
Preferred Stock are not paid in full, the holders of the Preferred Stock of such
series and of such other shares of preferred stock of the Company will share
ratably in any such distribution of assets of the Company in proportion to the
full respective preferential amounts to which they are entitled. After payment
to the holders of the Preferred Stock
 
                                       17
<PAGE>   29
 
of each series of the full preferential amounts of the liquidating distribution
to which they are entitled, the holders of each such series of the Preferred
Stock will be entitled to no further participation in any distribution of assets
by the Company.
 
REDEMPTION
 
     A series of the Preferred Stock may be redeemable, in whole or from time to
time in part, at the option of the Company, and may be subject to mandatory
redemption pursuant to a sinking fund or otherwise, in each case upon terms, at
the times and at the redemption prices set forth in the Prospectus Supplement
relating to such series. Unless otherwise provided in the applicable Prospectus
Supplement, shares of the Preferred Stock redeemed by the Company will be
restored to the status of authorized but unissued shares of preferred stock of
the Company.
 
     In the event that fewer than all of the outstanding shares of a series of
the Preferred Stock are to be redeemed, whether by mandatory or optional
redemption, the number of shares to be redeemed will be determined by lot or pro
rata (subject to rounding to avoid fractional shares) as may be determined by
the Company or by any other method as may be determined by the Company in its
sole discretion to be equitable. From and after the redemption date (unless
default is made by the Company in providing for the payment of the redemption
price plus accumulated and unpaid dividends, if any) dividends will cease to
accumulate on the shares of the Preferred Stock called for redemption and all
rights of the holders thereof (except the right to receive the redemption price
plus accumulated and unpaid dividends, if any) will cease.
 
     Unless otherwise specified in the applicable Prospectus Supplement, so long
as any dividends on shares of any series of the Preferred Stock or any other
series of preferred stock of the Company ranking on a parity as to dividends and
distribution of assets with such series of the Preferred Stock are in arrears,
no shares of any such series of the Preferred Stock or such other series of
preferred stock of the Company will be redeemed (whether by mandatory or
optional redemption) unless all such shares are simultaneously redeemed, and the
Company will not purchase or otherwise acquire any such shares; provided,
however, that the foregoing will not prevent the purchase or acquisition of such
shares pursuant to a purchase or exchange offer made on the same terms to
holders of all such shares outstanding.
 
CONVERSION RIGHTS
 
     The terms, if any, on which shares of Preferred Stock of any series may be
exchanged for or converted (mandatorily or otherwise) into shares of Common
Stock or another series of Preferred Stock will be set forth in the Prospectus
Supplement relating thereto. See "Description of Common Stock."
 
VOTING RIGHTS
 
     Except as indicated below or in a Prospectus Supplement relating to a
particular series of the Preferred Stock, or except as required by applicable
law, the holders of the Preferred Stock will not be entitled to vote for any
purpose.
 
     Unless otherwise specified in the applicable Prospectus Supplement, so long
as any shares of the Preferred Stock of a series remain outstanding, the consent
or the affirmative vote of the holders of at least a majority of the votes
entitled to be cast with respect to the then outstanding shares of such series
of the Preferred Stock together with any Other Preferred Stock (as defined
below), voting as one class, either expressed in writing or at a meeting called
for that purpose, will be necessary (a) to permit, effect or validate the
authorization, or any increase in the authorized amount, of any class or series
of shares of the Company ranking prior to the Preferred Stock of such series as
to dividends, voting or upon distribution of assets and (b) to repeal, amend or
otherwise change any of the provisions applicable to the Preferred Stock of such
series in any manner which adversely affects the powers, preferences, voting
power or other rights or privileges of such series of the Preferred Stock. In
case any series of the Preferred Stock would be so affected by any such action
referred to in clause (b) above in a different manner than one or more series of
the Other Preferred Stock then outstanding, the holders of shares of the
Preferred Stock of such series, together with any series of the Other Preferred
Stock which will be similarly affected, will be entitled to vote as a class, and
the Company
 
                                       18
<PAGE>   30
 
will not take such action without the consent or affirmative vote, as above
provided, of at least a majority of the total number of votes entitled to be
cast with respect to each such series of the Preferred Stock and the Other
Preferred Stock, then outstanding, in lieu of the consent or affirmative vote
hereinabove otherwise required.
 
     Unless otherwise specified in the applicable Prospectus Supplement, with
respect to any matter as to which the Preferred Stock of any series is entitled
to vote, holders of the Preferred Stock of such series and any other series of
preferred stock of the Company ranking on a parity with such series of the
Preferred Stock as to dividends and distributions of assets and which by its
terms provides for similar voting rights (the "Other Preferred Stock") will be
entitled to cast the number of votes set forth in the Prospectus Supplement with
respect to that series of Preferred Stock. As a result of the provisions
described in the preceding paragraph requiring the holders of shares of a series
of the Preferred Stock to vote together as a class with the holders of shares of
one or more series of Other Preferred Stock, it is possible that the holders of
such shares of Other Preferred Stock could approve action that would adversely
affect such series of Preferred Stock, including the creation of a class of
capital stock ranking prior to such series of Preferred Stock as to dividends,
voting or distributions of assets.
 
     As more fully described below under "Description of Depositary Shares," if
the Company elects to issue Depositary Shares, each representing a fraction of a
share of a series of the Preferred Stock, each such Depositary Share will, in
effect, be entitled to such fraction of a vote per Depositary Share.
 
TRANSFER AGENT AND REGISTRAR
 
     Unless otherwise indicated in a Prospectus Supplement relating thereto, the
Company will be the transfer agent, dividend and redemption price disbursement
agent and registrar for shares of each series of the Preferred Stock.
 
                        DESCRIPTION OF DEPOSITARY SHARES
 
     The description set forth below and in any Prospectus Supplement of certain
provisions of the Deposit Agreement (as defined below) and of the Depositary
Shares and Depositary Receipts does not purport to be complete and is subject to
and qualified in its entirety by reference to the Deposit Agreement and
Depositary Receipts relating to each series of the Preferred Stock which will be
filed with the Commission and incorporated by reference as an exhibit to the
Registration Statement of which this Prospectus is a part at or prior to the
time of the issuance of such series of the Preferred Stock. The forms of Deposit
Agreement and Depositary Receipt are filed as exhibits to the Registration
Statement of which this Prospectus is a part.
 
GENERAL
 
     The Company may, at its option, elect to offer fractional shares of
Preferred Stock rather than full shares of Preferred Stock. In the event such
option is exercised, the Company will issue to the public receipts for
Depositary Shares, each of which will represent a fraction (to be set forth in
the Prospectus Supplement relating to a particular series of the Preferred
Stock) of a share of a particular series of the Preferred Stock as described
below.
 
     The shares of any series of the Preferred Stock represented by Depositary
Shares will be deposited under a separate deposit agreement (the "Deposit
Agreement") among the Company, a bank or trust company selected by the Company
(the "Depositary") and the holders from time to time of the Depositary Receipts.
Subject to the terms of the Deposit Agreement, each owner of a Depositary Share
will in general be entitled, in proportion to the applicable fraction of a share
of Preferred Stock represented by such Depositary Share, to all the rights and
preferences of the Preferred Stock represented thereby (including dividend,
voting, redemption and liquidation rights).
 
     The Depositary Shares relating to any series of the Preferred Stock will be
evidenced by Depositary Receipts issued pursuant to the related Deposit
Agreement. Depositary Receipts will be distributed to those persons purchasing
such Depositary Shares in accordance with the terms of the offering made by the
related Prospectus Supplement.
 
                                       19
<PAGE>   31
 
     Upon surrender of Depositary Receipts at the office of the Depositary and
upon payment of the charges provided in the Deposit Agreement and subject to the
terms thereof, a holder of Depositary Receipts is entitled to have the
Depositary deliver to such holder the whole shares of Preferred Stock underlying
the Depositary Shares evidenced by the surrendered Depositary Receipts. However,
there may be no market for the underlying Preferred Stock and once the
underlying Preferred Stock is withdrawn from the Depositary, it may not be
redeposited.
 
DIVIDENDS AND OTHER DISTRIBUTIONS
 
     The Depositary will distribute all cash dividends or other cash
distributions received in respect of the Preferred Stock to the record holders
of Depositary Receipts relating to such Preferred Stock in proportion, insofar
as practicable, to the respective numbers of Depositary Shares evidenced by such
Depositary Receipts held by such holders on the relevant record date. The
Depositary will distribute only such amount, however, as can be distributed
without attributing to any holder of Depositary Receipts a fraction of one cent,
and any balance not so distributed will be added to and treated as part of the
next sum received by the Depositary for distribution to record holders of
Depositary Receipts then outstanding.
 
     In the event of a distribution other than in cash, the Depositary will
distribute such amounts of the securities or property received by it as are, as
nearly as practicable, in proportion to the respective numbers of Depositary
Shares evidenced by the Depositary Receipts held by such holders on the relevant
record date, unless the Depositary determines that it is not feasible to make
such distribution, in which case the Depositary may, with the approval of the
Company, adopt such method as it deems equitable and practicable for the purpose
of effecting such distribution, including the sale of such securities or
property.
 
     The Deposit Agreement will also contain provisions relating to the manner
in which any subscription or similar rights offered by the Company to holders of
the Preferred Stock will be made available to holders of Depositary Receipts.
 
     The amount distributed in all of the foregoing cases will be reduced by any
amounts required to be withheld by the Company or the Depositary on account of
taxes and governmental charges.
 
REDEMPTION OF DEPOSITARY SHARES
 
     If a series of the Preferred Stock represented by Depositary Shares is
subject to redemption, the Depositary Shares will be redeemed from the proceeds
received by the Depositary resulting from the redemption, in whole or in part,
of such series of the Preferred Stock held by the Depositary. The Depositary
will mail notice of redemption not less than 30 and not more than 60 days prior
to the date fixed for redemption to the record holders of the Depositary
Receipts evidencing the Depositary Shares to be so redeemed at their respective
addresses appearing in the Depositary's books. The redemption price per
Depositary Share will be equal to the applicable fraction of the redemption
price per share payable with respect to such series of the Preferred Stock plus
all money and other property, if any, payable with respect to such Depositary
Share, including all amounts payable by the Company in respect of any
accumulated but unpaid dividends. Whenever the Company redeems shares of
Preferred Stock held by the Depositary, the Depositary will redeem as of the
same redemption date the number of Depositary Shares representing shares of
Preferred Stock so redeemed. If less than all the Depositary Shares are to be
redeemed, the Depositary Shares to be redeemed will be selected by lot or pro
rata (subject to rounding to avoid fractions of Depositary Shares) as may be
determined by the Depositary.
 
     After the date fixed for redemption, the Depositary Shares so called for
redemption will no longer be deemed to be outstanding and all rights of the
holders of Depositary Receipts evidencing such Depositary Shares will cease,
except the right to receive the moneys payable upon such redemption and any
moneys or other property to which such holders were entitled upon such
redemption upon surrender to the Depositary of the Depositary Receipts
evidencing such Depositary Shares.
 
                                       20
<PAGE>   32
 
VOTING THE PREFERRED STOCK
 
     Upon receipt of notice of any meeting or action to be taken by written
consent at or as to which the holders of the Preferred Stock are entitled to
vote or consent, the Depositary will mail the information contained in such
notice of meeting or action to the record holders of the Depositary Receipts
evidencing the Depositary Shares relating to such Preferred Stock. Each record
holder of such Depositary Receipts on the record date (which will be the same
date as the record date for the Preferred Stock) will be entitled to instruct
the Depositary as to the exercise of the voting rights or the giving or refusal
of consent, as the case may be, pertaining to the number of shares of the
Preferred Stock represented by the Depositary Shares evidenced by such holder's
Depositary Receipts. The Depositary will endeavor, insofar as practicable, to
vote, or give or withhold consent with respect to, the maximum number of whole
shares of the Preferred Stock represented by all Depositary Shares as to which
any particular voting or consent instructions are received, and the Company will
agree to take all action which may be deemed necessary by the Depositary in
order to enable the Depositary to do so. The Depositary will abstain from
voting, or giving consents with respect to, shares of the Preferred Stock to the
extent it does not receive specific instructions from the holders of Depositary
Receipts evidencing Depositary Shares representing such Preferred Stock.
 
AMENDMENT AND TERMINATION OF THE DEPOSIT AGREEMENT
 
     The form of Depositary Receipt evidencing the Depositary Shares relating to
any series of Preferred Stock and any provision of the related Deposit Agreement
may at any time and from time to time be amended by agreement between the
Company and the Depositary in any respect which they may deem necessary or
desirable. However, any amendment which imposes or increases any fees, taxes or
charges upon holders of Depositary Shares or Depositary Receipts relating to any
series of Preferred Stock or which materially and adversely alters the existing
rights of such holders will not be effective unless such amendment has been
approved by the record holders of Depositary Receipts evidencing at least a
majority of such Depositary Shares then outstanding. Notwithstanding the
foregoing, no such amendment may impair the right of any holder of Depositary
Shares or Depositary Receipts to receive any moneys or other property to which
such holder may be entitled under the terms of such Depositary Receipts or the
Deposit Agreement at the times and in the manner and amount provided for
therein. A Deposit Agreement may be terminated by the Company or the Depositary
only after (a) all outstanding Depositary Shares relating thereto have been
redeemed and any accumulated and unpaid dividends on the Preferred Stock
represented by the Depositary Shares, together with all other moneys and
property, if any, to which holders of the related Depositary Receipts are
entitled under the terms of such Depositary Receipts or the related Deposit
Agreement, have been paid or distributed as provided in the Deposit Agreement or
provision therefor has been duly made, (b) there has been a final distribution
in respect of the Preferred Stock of the relevant series in connection with any
liquidation, dissolution or winding up of the Company and such distribution has
been distributed to the holders of the related Depositary Receipts, or (c) in
the event the Depositary Shares relate to a series of Preferred Stock which is
convertible into shares of Common Stock or another series of Preferred Stock,
all outstanding Depositary Shares have been converted into shares of Common
Stock or another series of Preferred Stock.
 
MISCELLANEOUS
 
     The Depositary will forward to record holders of Depositary Receipts, at
their respective addresses appearing in the Depositary's books, all reports and
communications from the Company which are delivered to the Depositary and which
the Company is required to furnish to the holders of the Preferred Stock or
Depositary Receipts.
 
     The Company will pay all transfer and other taxes and governmental charges
arising solely from the existence of the depositary arrangements. The Company
will pay charges of the Depositary in connection with the initial deposit of the
Preferred Stock and the initial issuance of the Depositary Receipts evidencing
the Depositary Shares, any redemption of the Preferred Stock and any withdrawals
of Preferred Stock by the holders of Depositary Shares. Holders of Depositary
Shares will pay other transfer and other taxes and
 
                                       21
<PAGE>   33
 
governmental charges and such other charges as are expressly provided in the
Deposit Agreement to be for their accounts.
 
     The Deposit Agreement will contain provisions relating to adjustments in
the fraction of a share of Preferred Stock represented by a Depositary Share in
the event of a change in par value, split-up, combination or other
reclassification of the Preferred Stock or upon any recapitalization, merger or
sale of substantially all of the assets of the Company as an entirety.
 
     Neither the Depositary nor any of its agents nor any registrar nor the
Company will be (a) liable if it is prevented or delayed by law or any
circumstance beyond its control in performing its obligations under the Deposit
Agreement, (b) subject to any liability under the Deposit Agreement to holders
of Depositary Receipts other than for the relevant party's gross negligence or
willful misconduct, or (c) obligated to prosecute or defend any legal proceeding
in respect of any Depositary Receipts, Depositary Shares or the Preferred Stock
unless satisfactory indemnity is furnished. They may rely upon written advice of
counsel or accountants, or information provided by holders of Depositary
Receipts or other persons in good faith believed to be competent and on
documents reasonably believed to be genuine.
 
RESIGNATION OR REMOVAL OF DEPOSITARY
 
     The Depositary may resign at any time by delivering to the Company notice
of its election to do so, and the Company may at any time remove the Depositary,
any such resignation or removal to take effect upon the appointment of a
successor Depositary and its acceptance of such appointment. Such successor
Depositary must be appointed within 60 days after delivery of the notice of
resignation or removal.
 
                          DESCRIPTION OF COMMON STOCK
GENERAL
 
     The holders of the outstanding shares of Common Stock have full voting
rights, one vote for each share held of record. Shareholders have cumulative
voting rights with respect to the election of directors, if certain conditions
are met. Upon liquidation, dissolution, or winding up of the Company (but
subject to the rights of holders of preferred stock of the Company, Cumulative
Preferred Stock and Preference Stock), the assets legally available for
distribution to holders of Common Stock will be distributed ratably among such
holders. Holders of Common Stock have no preemptive or other subscription or
conversion rights, and no liability for further calls upon shares. The Common
Stock is not subject to assessment. Shares of Common Stock may be issued in
series with a special initial dividend rate as hereinafter described (any such
series, being referred to herein as "Special Common Stock"). No shares of
Special Common Stock are outstanding and the Company does not intend to offer
such securities in the future.
 
     Subject to the rights of holders of preferred stock of the Company,
Cumulative Preferred Stock and Preference Stock, holders of Common Stock are
entitled to receive such dividends as may be declared by the Board of Directors
of the Company out of funds legally available therefor. Dividends on all series
of Common Stock must have the same record and payment dates. No series of Common
Stock may have preference over any other series as to the payment of dividends,
but the amount of cash dividends paid may vary among series.
 
     Under the terms of the Articles of Incorporation, the initial dividend rate
on any Special Common Stock issued by the Company must be established by the
Board of Directors of the Company at or before the issuance thereof at an annual
rate greater than four times the last quarterly dividend paid on Common Stock
which is not Special Common Stock (referred to herein as "Original Common
Stock").
 
     The initial dividend rate on each share of Special Common Stock must be
reduced if the quarterly dividend on a share of Original Common Stock is reduced
and on the same percentage basis. The initial dividend rate on each share of
Special Common Stock must also be increased if the dividend on a share of
Original Common Stock is increased and on the same percentage basis; provided
that at no time may the dividend on a share of Special Common Stock of any
series exceed the greater of (a) one-fourth of the initial
 
                                       22
<PAGE>   34
 
annual dividend rate established at the time of issuance of any such share of
Special Common Stock, or (b) the dividend rate concurrently being paid on each
of the outstanding shares of Original Common Stock. Shares of Special Common
Stock of any series will cease to be shares of Special Common Stock (and will
thereafter be considered to be shares of Original Common Stock) at any time that
the aggregate of all dividends paid during any fiscal year on shares of Special
Common Stock of that series fails to exceed the aggregate of all dividends paid
by the Company during such year on each share of Original Common Stock.
 
     The Company is the transfer agent and registrar for the Common Stock.
 
CERTAIN PROVISIONS OF THE ARTICLES OF INCORPORATION AND BYLAWS
 
     The Company's Articles of Incorporation contain provisions which require a
super-majority vote of the holders of Common Stock in order for certain types of
business combinations to be approved. These provisions are applicable to (a) any
merger or consolidation of the Company with or into a dominant stockholder (as
hereinafter defined) or any entity controlled by a dominant stockholder, (b) any
merger of a dominant stockholder with or into the Company or any corporation
controlled by or under common control with the Company, (c) any sale, lease,
exchange or transfer of all or substantially all of the property and assets of
the Company to a dominant stockholder or any entity controlled by or under
common control with a dominant stockholder, (d) any purchase, lease, exchange,
transfer or acquisition by the Company of all or substantially all of the
property and assets of a dominant stockholder or any entity controlled by or
under common control with a dominant stockholder, (e) any recapitalization of
the Company that would have the effect of increasing the voting power of a
dominant stockholder, and (f) any agreement, contract or other arrangement
providing for any of the foregoing. The term "dominant stockholder" is defined
as any person that, together with any affiliate or associate, beneficially owns
in the aggregate 10% or more of the outstanding Common Stock of the Company.
 
     The affirmative vote of not fewer than 85% of the outstanding shares of
Common Stock must approve a business combination, unless (a) the Board of
Directors of the Company has approved the business combination by the
affirmative vote of (i) not fewer than 65% of its members if the business
combination is approved in advance of the dominant stockholder becoming a
dominant stockholder or the acquisition of shares of Common Stock that caused
the dominant stockholder to become a dominant stockholder has been approved in
advance, or (ii) not fewer than 85% of its members in all other circumstances,
or (b) the Board of Directors of the Company by an affirmative vote of not fewer
than 85% has determined that the cash or fair value of the properties,
securities or other consideration to be received by the holders of Common Stock
in the business combination is not less than the highest per share price paid by
the dominant stockholder in acquiring any of its holdings of the Common Stock.
These provisions may only be amended by an affirmative vote of 65% of the
outstanding shares of the Company's Common Stock, unless there is a dominant
stockholder at the time of the vote, in which event a vote of 85% of the
outstanding shares of Common Stock is required.
 
     California law permits corporations to limit or eliminate the personal
liability of their directors in any action, including actions brought by the
corporation or its shareholders for monetary damages for breach of a director's
fiduciary duty of care. The duty of care requires that, when acting on behalf of
the corporation, a director must act in good faith, in a manner such director
believes to be in the best interests of the corporation and its shareholders and
with such care, including reasonable inquiry, as an ordinarily prudent person in
a like position would use under similar circumstances. As a result, the
available relief to a corporation and its shareholders may be limited to
equitable remedies such as injunction or rescission if a company indemnifies its
directors to the fullest extent permitted by California law.
 
     Article VIII of the Company's Articles of Incorporation and Bylaws limit
the liability of directors of the Company to the Company or its shareholders (in
their capacity as directors, but not in their capacity as officers) to the
fullest extent permitted by California law. Specifically, directors of the
Company are not personally liable to the Company or its shareholders for
monetary damages for breach of a director's fiduciary duty as a director, except
(a) on account of profits made in connection with a purchase or sale of
securities in violation of Section 16(b) of the Exchange Act, (b) if a court of
competent jurisdiction determines that indemnification is unlawful, (c) for acts
or omissions involving intentional misconduct or knowing and
 
                                       23
<PAGE>   35
 
culpable violations of law, (d) for acts or omissions that the director believed
to be contrary to the best interests of the Company or its shareholders or that
involve the absence of good faith on the part of the director, (e) for any
transaction for which the director derived an improper benefit, (f) for acts or
omissions that show a reckless disregard for the director's duty to the Company
or its shareholders in circumstances in which the director was aware, or should
have been aware, in the ordinary course of performing his or her duties, of a
risk of serious injury to the Company or its shareholders, (g) for acts or
omissions that constitute an unexcused pattern of inattention that amounts to an
abdication of the director's duties to the corporation or its shareholders, (h)
for liabilities arising out of transactions in which the director had a personal
interest, (i) for the approval of distributions to the Company's shareholders in
violation of California law, or (j) for the approval of the making by the
Company of any loan of money or property to a director or officer of the Company
or the guarantee of the obligations of any such director or officer in violation
of California law. The inclusion of these provisions in the Company's Articles
of Incorporation and Bylaws may have the effect of reducing the likelihood of
litigation against directors of the Company, even though such an action, if
successful, might otherwise have benefited the Company or its shareholders.
 
CERTAIN PROVISIONS OF STATE AND FEDERAL LAW
 
     Arizona regulates certain business combinations by an "interested
shareholder" of a public corporation if the public corporation (a) has issued
securities under Section 12 of the Exchange Act, (b) has its principal place of
business in the State of Arizona, (c) owns or controls assets located within the
State of Arizona with a fair market value of at least one million dollars, and
(d) has more than 500 employees in the State of Arizona. The Company believes
that these provisions are currently applicable to the Company. A person becomes
an interested shareholder under the Arizona business combination statute upon
the acquisition of 10% or more of the outstanding voting shares of the public
corporation. The term "business combination" is broadly defined to include not
only acquisitions, but also restructuring transactions and transactions in which
the interested shareholder, or its associates or affiliates, receive financial
assistance or tax advantages from the public corporation. Business combinations
must be approved by a majority of the members of a committee of disinterested
directors in advance of the interested person becoming an interested person or
the consummation of the business combination must be delayed for three years and
the price to be paid must meet certain fair price criteria. The committee must
consider the long term interests of the public corporation in connection with
approving any such transaction. Additional restrictions are applicable to
acquisitions of control of 20% or more of a public corporation's voting stock.
 
     Under California law, if a tender offer or a written proposal for approval
of a reorganization of a corporation or a sale of substantially all of its
assets is made by an "interested party", an affirmative opinion in writing as to
the fairness of the consideration to be received by the shareholders must be
delivered to each shareholder. The term "interested party" means a person who is
a party to the transaction and who (a) directly or indirectly controls the
corporation that is the subject of the tender offer or proposal, (b) is, or is
directly or indirectly controlled by, an officer or director of the corporation,
or (c) is an entity in which a material financial interest is held by any
director or executive officer.
 
     No public utility or any of its affiliates may acquire any of the capital
stock of a public utility organized under California law, without CPUC approval,
if (a) the acquiror transacts business in California, or (b) the CPUC determines
that CPUC approval is otherwise required by the public interest. In addition, a
change in control application must be filed with the CPUC in connection with any
change in control of a public utility organized under California law. PSCN
approval is also required prior to any proposed transfer of 15% or more of the
common stock of a public utility doing business in Nevada.
 
     No person may acquire 5% or more of the voting stock of a gas utility
(other than by merger), without Securities and Exchange Commission (the
"Commission") approval, if such person owns 5% or more of the stock of another
public utility or public utility holding company. A registered public utility
holding company may not acquire any security of another gas utility without
Commission approval, unless the transaction is exempt under the Public Utility
Holding Company Act of 1935, as amended (the "PUHCA"), or the regulations
promulgated thereunder. A person becomes a holding company required to be
registered under PUHCA upon acquisition of 10% or more of the voting stock of a
gas utility, unless the Commission determines that the person does not control
the gas utility. The Commission may condition any such
 
                                       24
<PAGE>   36
 
determination upon the applicant refraining from exercising voting rights,
controlling proxies or designating officers or directors. The Commission may not
approve the acquisition of securities of a gas utility unless it determines that
the acquisition would tend toward the economical and efficient development of an
integrated public utility system and would not be detrimental to investor
interests. The Commission may also condition its approval of the acquisition of
the securities of a gas utility upon a fair offer being made for the other
securities of the utility.
 
     In addition to being a gas utility, the Company is also a savings and loan
holding company. No person may acquire control of a savings and loan holding
company without the prior approval of the OTS, unless the transaction is exempt.
A person is conclusively deemed to have obtained control of a savings and loan
holding company if it (a) has acquired any combination of voting stock and
irrevocable proxies representing more than 25% of any class of voting stock of
the savings and loan holding company, or (b) controls in any manner the election
of a majority of the directors of the savings and loan holding company or
savings and loan association. A person who has acquired more than 10% of any
class of voting stock of the savings and loan holding company may also be deemed
to have control of the savings and loan holding company if certain control
factors are present.
 
                              PLAN OF DISTRIBUTION
 
     The Company may sell the Securities to one or more underwriters for public
offering and sale by them or may sell the Securities to investors directly or
through agents. Any such underwriter or agent involved in the offer and sale of
Securities will be named in the applicable Prospectus Supplement. The Company
has reserved the right to sell Securities directly to investors on its own
behalf in those jurisdictions where and in such manner as it is authorized to do
so.
 
     Underwriters may offer and sell Securities at a fixed price or prices,
which may be changed, at market prices prevailing at the time of sale, at prices
related to such prevailing market prices or at negotiated prices. The Company
also may, from time to time, authorize dealers, acting as the Company's agents,
to offer and sell Securities upon the terms and conditions as are set forth in
the applicable Prospectus Supplement. In connection with the sale of Securities,
underwriters may receive compensation from the Company in the form of
underwriting discounts or commissions and may also receive commissions from
purchasers of the Securities for whom they may act as agent. Underwriters may
sell Securities to or through dealers, and such dealers may receive compensation
in the form of discounts, concessions or commissions from the underwriters
and/or commissions from the purchasers for whom they may act as agent.
 
     Any underwriting compensation paid by the Company to underwriters or agents
in connection with the offering of Securities, and any discounts, concessions or
commissions allowed by underwriters to participating dealers, will be set forth
in the applicable Prospectus Supplement. Dealers and agents participating in the
distribution of Securities may be deemed to be underwriters, and any discounts
and commissions received by them and any profit realized by them on resale of
the Securities may be deemed to be underwriting discounts and commissions.
Underwriters, dealers and agents may be entitled, under agreements entered into
with the Company, to indemnification against and contribution toward certain
civil liabilities.
 
     Securities may also be offered and sold, if so indicated in the Prospectus
Supplement, in connection with a remarketing upon their purchase, in accordance
with a redemption or repayment pursuant to their terms, or otherwise, by one or
more firms ("remarketing firms"), acting as principals for their own accounts or
as agents for the Company. Any remarketing firm will be identified and the terms
of its agreement, if any, with the Company and its compensation will be
described in the applicable Prospectus Supplement. Remarketing firms may be
deemed to be underwriters in connection with the Securities remarketed thereby.
Remarketing firms may be entitled under agreements which may be entered into
with the Company to indemnification by the Company against certain liabilities,
including liabilities under the Securities Act of 1933, and may be customers of,
engage in transactions with or perform services for the Company in the ordinary
course of business.
 
                                       25
<PAGE>   37
 
                                 LEGAL MATTERS
 
     The validity of the Offered Securities will be passed upon for the Company
by O'Melveny & Myers.
 
                                    EXPERTS
 
     The consolidated financial statements incorporated by reference in this
Prospectus have been audited by Arthur Andersen LLP, independent public
accountants, as indicated in their report included in the Annual Report on Form
10-K for the year ended December 31, 1994, and are included herein in reliance
upon the authority of said firm as experts in accounting and auditing in giving
said report.
 
                                       26
<PAGE>   38
 
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  NO DEALER, SALESPERSON OR OTHER INDIVIDUAL HAS BEEN AUTHORIZED TO GIVE
INFORMATION OR TO MAKE ANY REPRESENTATIONS NOT CONTAINED IN THIS PROSPECTUS
SUPPLEMENT AND THE PROSPECTUS IN CONNECTION WITH THE OFFER MADE BY THIS
PROSPECTUS SUPPLEMENT AND THE PROSPECTUS AND, IF GIVEN OR MADE, SUCH INFORMATION
OR REPRESENTATIONS MUST NOT BE RELIED UPON AS HAVING BEEN AUTHORIZED BY THE
COMPANY OR THE UNDERWRITERS. NEITHER THE DELIVERY OF THIS PROSPECTUS SUPPLEMENT
AND THE PROSPECTUS NOR ANY SALE MADE HEREUNDER AND THEREUNDER SHALL UNDER ANY
CIRCUMSTANCE CREATE AN IMPLICATION THAT THERE HAS BEEN NO CHANGE IN THE AFFAIRS
OF THE COMPANY SINCE THE DATE HEREOF. THIS PROSPECTUS SUPPLEMENT AND THE
PROSPECTUS DO NOT CONSTITUTE AN OFFER OR SOLICITATION BY ANYONE IN ANY STATE IN
WHICH SUCH OFFER OR SOLICITATION BY ANYONE IN ANY STATE IN WHICH SUCH OFFER OR
SOLICITATION IS NOT AUTHORIZED OR IN WHICH THE PERSON MAKING SUCH OFFER OR
SOLICITATION IS NOT QUALIFIED TO DO SO OR TO ANYONE TO WHOM IT IS UNLAWFUL TO
MAKE SUCH OFFER OR SOLICITATION.
                            ------------------------
 
                               TABLE OF CONTENTS
 
                             PROSPECTUS SUPPLEMENT
 
<TABLE>
<CAPTION>
                                             PAGE
                                             ----
<S>                                          <C>
The Company...............................    S-2
Recent Developments.......................    S-3
Ratios of Earnings to Fixed Charges.......    S-3
Selected Financial Information............    S-4
Capitalization............................    S-5
Use of Proceeds...........................    S-6
Capital Expenditures and Financing
  Programs................................    S-6
Description of Debentures.................    S-6
Underwriting..............................   S-11
Legal Matters.............................   S-11
Experts...................................   S-11
                   PROSPECTUS
Available Information.....................      2
Incorporation of Certain Documents by
  Reference...............................      2
The Company...............................      3
The Trust.................................      3
Use of Proceeds...........................      4
Ratios of Earnings to Fixed Charges.......      5
Description of Debt Securities............      5
Particular Terms of Subordinated Debt
    Securities Issued in Connection with
      Preferred Securities................     11
Description of the Preferred Securities...     12
Description of the Guarantee..............     13
Description of Preferred Stock............     15
Description of Depositary Shares..........     19
Description of Common Stock...............     22
Plan of Distribution......................     25
Legal Matters.............................     26
Experts...................................     26
</TABLE>
 
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                                  $150,000,000
 
                                 SOUTHWEST GAS
                                  CORPORATION
   
                     $75,000,000 7 1/2% DEBENTURES DUE 2006
    
   
                       $75,000,000 8% DEBENTURES DUE 2026
    
                                 (R)  LOGO
                           -------------------------
 
                             PROSPECTUS SUPPLEMENT
                           -------------------------
 
                              MERRILL LYNCH & CO.
                            PAINEWEBBER INCORPORATED
   
                                 JULY 31, 1996
    
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