<PAGE>   1
                                                                      EXHIBIT 3A

                                    RESTATED

                          CERTIFICATE OF INCORPORATION

                                       OF

                           EL PASO NATURAL GAS COMPANY


         E1 Paso Natural Gas Company, a corporation organized and existing under
the General Corporation Law of the State of Delaware, does hereby certify:

         1. The original Certificate of Incorporation was filed with the
Secretary of State on November 28, 1928. The name under which it was originally
incorporated is El Paso Natural Gas Company.

         2. The following Restated Certificate of Incorporation was duly
proposed by the corporation's Board of Directors pursuant to the applicable
provisions of Section 242 and Section 245 of the General Corporation Law of the
State of Delaware. In lieu of a meeting of the stockholders, unanimous written
consent has been given for the adoption of said Restated Certificate of
Incorporation and the amendments to be made thereby pursuant to the applicable
provisions of Sections 228, 242 and 245 of the General Corporation Law of the
State of Delaware.


                                 ARTICLE 1. NAME

         The name of this corporation is EL PASO NATURAL GAS COMPANY.


                     ARTICLE 2. REGISTERED OFFICE AND AGENT

         The address of the registered office of this corporation is Corporation
Trust Center, 1209 Orange Street, City of Wilmington, County of New Castle,
State of Delaware 19801, and the name of its registered agent at such address is
The Corporation Trust Company.


                               ARTICLE 3. PURPOSES

         The purpose of this corporation is to engage in any lawful act or
activity for which corporations may be organized under the General Corporation
Law of the State of Delaware.



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                                ARTICLE 4. SHARES

         The total number of authorized shares of all classes of stock of this
corporation consist of 100,000,000 shares of common stock having a par value of
$3 per share and 25,000,000 shares of preferred stock having a par value of $.01
per share. Authority is hereby expressly granted to the Board of Directors to
fix by resolution or resolutions any of the designations and the powers,
preferences and rights, and the qualifications, limitations or restrictions
which are permitted by the General Corporation Law of the State of Delaware in
respect of any class or classes of stock or any series of any class of stock of
the corporation.


                               ARTICLE 5. BY-LAWS

         The Board of Directors shall have the power to adopt, amend or repeal
the By-laws of this corporation, subject to the power of the stockholders to
amend or repeal such By-laws. The stockholders having voting power shall also
have the power to adopt, amend or repeal the By-laws of this corporation.


                        ARTICLE 6. ELECTION OF DIRECTORS

         Except as may be otherwise required by the By-laws, written ballots are
not required in the election of Directors.


                          ARTICLE 7. PREEMPTIVE RIGHTS

         Preemptive rights shall not exist with respect to shares of stock or
securities convertible into shares of stock of this corporation.


                          ARTICLE 8. CUMULATIVE VOTING

         The right to cumulate votes in the election of Directors shall not
exist with respect to shares of stock of this corporation.


          ARTICLE 9. AMENDMENTS TO RESTATED CERTIFICATE OF INCORPORATION

         This corporation reserves the right to amend or repeal any of the
provisions contained in this Restated Certificate of Incorporation in any manner
now or hereafter permitted by law, and the rights of the stockholders of this
corporation are granted subject to this reservation.


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                  ARTICLE 10. LIMITATION OF DIRECTOR LIABILITY

         To the full extent that the General Corporation Law of the State of
Delaware, as it exists on the date hereof or may hereafter be amended, permits
the limitation or elimination of the liability of Directors, a Director of this
corporation shall not be liable to this corporation or its stockholders for
monetary damages for breach of fiduciary duty as a Director. Any amendment to or
repeal of this Article 10 shall not adversely affect any right or protection of
a Director of this corporation for or with respect to any acts or omissions of
such Director occurring prior to such amendment or repeal.


              ARTICLE 11. ACTION BY STOCKHOLDERS WITHOUT A MEETING

         Any action by the stockholders of this corporation shall be taken at a
meeting of stockholders and no action may be taken by written consent of
stockholders entitled to vote on such action.


                     ARTICLE 12. SPECIAL VOTING REQUIREMENTS

         In addition to any affirmative vote required by law, by this Restated
Certificate of Incorporation, by any agreement with any national securities
exchange, or as may be otherwise required, any "Business Combination" (as
hereinafter defined) involving this corporation shall be subject to approval in
the manner set forth in this Article 12.

         12.1 Definitions.

         For the purposes of this Article 12:

                  (a) "Affiliate" and "beneficial owner" are used herein as
         defined in Rule 12b-2 and Rule 13d-3, respectively, under the
         Securities Exchange Act of 1934 as in effect on January 1, 1992 (the
         "1934 Act"). The term "Affiliate" as used herein shall exclude this
         corporation, but shall include the definition of "Associate" as
         contained in said Rule 12b-2.

                  (b) An "Interested Stockholder" is a person other than (i) the
         corporation or (ii) Burlington Resources Inc., a Delaware corporation
         ("BRI"), as long as BRI continues to own at least a majority of the
         stock of this corporation entitled to vote for the election of
         Directors ("Voting Stock") and there has been no Change in Control of
         BRI since January 1, 1992, who is (A) the beneficial 



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         owner of ten percent or more of the Voting Stock or (B) an Affiliate of
         this corporation which (1) at any time within a two-year period prior
         to the record date for the vote on a Business Combination was the
         beneficial owner of ten percent or more of the Voting Stock, or (2) at
         the completion of the Business Combination will be the beneficial owner
         of ten percent or more of the Voting Stock.

                  (c) A "Person" is a natural person or a legal entity of any
         kind, together with any Affiliate of such person or entity, or any
         person or entity with whom such person, entity or any Affiliate has any
         agreement or understanding relating to acquiring, voting or holding
         Voting Stock.

                  (d) A "Disinterested Director" is a member of the Board of
         Directors of this corporation (other than the Interested Stockholder)
         who was a Director prior to the time the Interested Stockholder became
         an Interested Stockholder, or any Director who was recommended for
         election by the Disinterested Directors. Any action to be taken by the
         Disinterested Directors shall require the affirmative vote of at least
         two-thirds of the Disinterested Directors.

                  (e) A "Business Combination" is (i) a merger or consolidation
         of this corporation or any of its subsidiaries with an Interested
         Stockholder; (ii) the sale, lease, exchange, pledge, transfer or other
         disposition (A) by this corporation or any of its subsidiaries of all
         or a Substantial Part of the corporation's Assets to an Interested
         Stockholder, or (B) by an Interested Stockholder of any of its assets,
         except in the ordinary course of business, to this corporation or any
         of its subsidiaries; (iii) the issuance of stock or other securities of
         this corporation or any of its subsidiaries to an Interested
         Stockholder, other than on a pro rata basis to all holders of Voting
         Stock of the same class held by the Interested Stockholder pursuant to
         a stock spilt, stock dividend or distribution of warrants or rights;
         (iv) the adoption of any plan or proposal for the liquidation or
         dissolution of this corporation proposed by or on behalf of an
         Interested Stockholder; (v) any reclassification of securities,
         recapitalization, merger or consolidation or other transaction which
         has the effect, directly or indirectly, of increasing the proportionate
         share of any Voting Stock beneficially owned by an Interested
         Stockholder; or (vi) any agreement, contract or other arrangement
         providing for any of the foregoing transactions.

                  (f) A "Substantial Part of the corporation's Assets" shall
         mean assets of this corporation or any of its subsidiaries in an amount
         equal to twenty percent or more of the fair market value, as determined
         by the Disinterested Directors, of the total consolidated assets of
         this corporation and its subsidiaries taken as a whole as of the end of
         its most recent fiscal year ended prior to the time the determination
         is made.


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                  (g) A "Change in Control" shall be deemed to occur (i) if any
         Person is or becomes the "beneficial owner" (as defined in Rule 13d-3
         of the 1934 Act), directly or indirectly, of securities of BRI
         representing twenty percent or more of the stock of BRI entitled to
         vote for Directors of BRI, (ii) upon the first purchase of BRI's common
         stock pursuant to a tender or exchange offer (other than a tender or
         exchange offer made by BRI), (iii) upon the approval by BRI's
         stockholders of a merger or consolidation, a sale or disposition of all
         or substantially all of BRI's assets or a plan of liquidation or
         dissolution of BRI, or (iv) if, during any period of two consecutive
         years, individuals who at the beginning of such period constitute the
         BRI Board of Directors cease for any reason to constitute at least a
         majority thereof, unless the election or nomination of the election by
         BRI's stockholders of each new Director was approved by a vote of at
         least two-thirds of the Directors then still in office who were
         Directors at the beginning of the period.

         12.2  Vote Required for Business Combinations.

         The affirmative vote of not less than fifty-one percent of the Voting
Stock, excluding the Voting Stock of an Interested Stockholder who is a party to
the Business Combination, shall be required for the adoption or authorization of
a Business Combination, unless the Disinterested Directors determine that:

                  (a) The Interested Stockholder is the beneficial owner of not
         less than eighty percent of the Voting Stock and has declared its
         intention to vote in favor of or to approve such Business Combination;
         or

                  (b) (i) The fair market value of the consideration per share
         to be received or retained by the holders of each class or series of
         stock of this corporation in a Business Combination is equal to or
         greater than the consideration per share (including brokerage
         commissions and soliciting dealer's fees) paid by such Interested
         Stockholder in acquiring the largest number of shares of such class of
         stock previously acquired in any one transaction or series of related
         transactions, whether before or after the Interested Stockholder became
         an Interested Stockholder and (ii) the Interested Stockholder shall not
         have received the benefit, directly or indirectly (except
         proportionately as a stockholder), of any loans, advances, guarantees,
         pledges or other financial assistance provided by this corporation,
         whether in anticipation of or in connection with such Business
         Combination or otherwise.

         12.3  Information Requirements.

         In the event any vote of holders of Voting Stock is required for the
adoption or approval of any Business Combination, a proxy or information
statement describing the 



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Business Combination and complying with the requirements of the 1934 Act shall
be mailed at a date determined by the Disinterested Directors to all
stockholders of this corporation whether or not such statement is required under
the 1934 Act. The statement shall contain any recommendations as to the
advisability of the Business Combination which the Disinterested Directors, or
any of them, may choose to state and, if deemed advisable by the Disinterested
Directors, an opinion of an investment banking firm as to the fairness of the
terms of such Business Combination. Such firm shall be selected by the
Disinterested Directors and be paid a fee for its services by this corporation
as approved by the Disinterested Directors.

         12.4  Amendment.

         No amendment to this Restated Certificate of Incorporation shall amend,
alter, change or repeal any of the provisions of Article 11 or of this Article
12 unless such amendment shall receive the affirmative vote of not less than
fifty-one percent of the Voting Stock, excluding the Voting Stock of any
Interested Stockholder as defined in Section 12.1 of this Article 12.




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         IN WITNESS WHEREOF, the undersigned has executed this document and
affirms, under penalties of perjury, that the statements herein are true and
that this instrument is the act and deed of El Paso Natural Gas Company as of
this 22nd day of January, 1992.


                                    EL PASO NATURAL GAS COMPANY



                                        /s/ William A. Wise
                               -----------------------------------------
                                            William A. Wise
                                          President and Chief
                                           Executive Officer


Attest:


      /s/ Eldon J. Mitrisin
-----------------------------------------
          Eldon J. Mitrisin
         Assistant Secretary


STATE OF TEXAS             )
                           )  ss.
COUNTY OF HARRIS           )

         Be it remembered that on this 22nd day of January, 1992, personally
came before me, a Notary Public for the State of Texas, William A. Wise,
President and Chief Executive Officer of El Paso Natural Gas Company, known to
me to be such, and acknowledged the said Certificate to be the act and deed of
El Paso Natural Gas Company and that the facts stated therein are true.

         Given under my hand and seal of office the day and year aforesaid.


                                       /s/ Catherine M. Geisert
                               -----------------------------------------
                                              Notary Public

[Seal]


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                           Certificate of Designation,

                             Preferences and Rights

                  Series A Junior Participating Preferred Stock

                                       of

                           E1 Paso Natural Gas Company

                            (Pursuant to Section 151
            of the General Corporation Law of the State of Delaware)

         I, Britton White, Jr., Senior Vice President and General Counsel of E1
Paso Natural Gas Company (the "Company"), a corporation organized and existing
under the General Corporation Law of the State of Delaware, in accordance with
the provisions of Section 103 thereof, DO HEREBY CERTIFY as follows:

         That pursuant to the authority conferred upon the Board of Directors by
the Restated Certificate of Incorporation of the said Corporation, said Board of
Directors on July 7, 1992, adopted the following resolution creating a series of
1,000,000 shares of Preferred Stock designated as Series A Junior Participating
Preferred Stock:

         RESOLVED that pursuant to the authority granted to and vested in the
Board of Directors of this Company in accordance with the provisions of the
Restated Certificate of Incorporation, the Board of Directors hereby creates a
series of Preferred Stock of the Company and hereby states the designation and
number of shares, and fixes the relative rights, preferences and limitations
thereof (in addition to the provisions set forth in the Restated Certificate of
Incorporation which are applicable to the Preferred Stock of all classes and
series) as follows:

         Section 1.   Designation and Amount.   There shall be a series of
Preferred Stock, par value $.01 per share, of the Company which shall be
designated as "Series A Junior Participating Preferred Stock," par value $.01
per share, and the number of shares constituting such series shall be 1,000,000.
Such number of shares may be increased or decreased by resolution of the Board
of Directors; provided, that no decrease shall reduce the number of shares of
Series A Junior Participating Preferred Stock to a number less than that of the
shares then outstanding plus the number of shares issuable upon exercise of
outstanding rights, options or warrants or upon conversion of outstanding
securities issued by the Company.

         Section 2.   Dividends and Distributions.

         (A) Subject to the prior and superior rights of the holders of any
shares of any series of Preferred Stock ranking prior and superior to the Series
A Junior Participating Preferred Stock with respect to dividends, the holders of
shares of Series A Junior Participating Preferred Stock in preference to the
holders of shares of Common Stock, par value $3.00 per share (the 


<PAGE>   9

"Common Stock"), of the Company and any other junior stock, shall be entitled
to receive, when, as and if declared by the Board of Directors out of funds
legally available for the purpose, quarterly dividends payable in cash on the
first day of January, April, July, and October in each year (each such date
being referred to herein as a "Quarterly Dividend Payment Date"), commencing on
the first Quarterly Dividend Payment Date after the first issuance of a share or
fraction of a share of Series A Junior Participating Preferred Stock in an
amount per share (rounded to the nearest cent) equal to the greater of (a) $25,
or (b) subject to the provision for adjustment hereinafter set forth, 100 times
the aggregate per share amount of all cash dividends, and 100 times the
aggregate per share amount (payable in kind) of all non-cash dividends or other
distributions other than a dividend payable in shares of Common Stock or a
subdivision of the outstanding shares of Common Stock (by reclassification or
otherwise), declared on the Common Stock since the immediately preceding
Quarterly Dividend Payment Date, or, with respect to the first Quarterly
Dividend Payment Date, since the first issuance of any share or fraction of a
share of Series A Junior Participating Preferred Stock. In the event the Company
shall at any time after July 28, 1992 (the "Rights Declaration Date") (i)
declare any dividend on Common Stock payable in shares of Common Stock, (ii)
subdivide the outstanding Common Stock, or (iii) combine the outstanding Common
Stock into a smaller number of shares, then in each such case the amount to
which holders of shares of Series A Junior Participating Preferred Stock were
entitled immediately prior to such event under clause (b) of the preceding
sentence shall be adjusted by multiplying such amount by a fraction the
numerator of which is the number of shares of Common Stock outstanding
immediately after such event and the denominator of which is the number of
shares of Common Stock that were outstanding immediately prior to such event.

         (B) The Company shall declare a dividend or distribution on the Series
A Junior Participating Preferred Stock as provided in paragraph (A) above
immediately after it declares a dividend or distribution on the Common Stock
(other than a dividend payable in shares of Common Stock); provided that, in the
event no dividend or distribution shall have been declared on the Common Stock
during the period between any Quarterly Dividend Payment Date and the next
subsequent Quarterly Dividend Payment Date, a dividend of $25 per share on the
Series A Junior Participating Preferred Stock shall nevertheless be payable on
such subsequent Quarterly Dividend Payment Date.

         (C) Dividends shall begin to accrue and be cumulative on outstanding
shares of Series A Junior Participating Preferred Stock from the Quarterly
Dividend Payment Date next preceding the date of issue of such shares of Series
A Junior Participating Preferred Stock unless the date of issue of such shares
is prior to the record date for the first Quarterly Dividend Payment Date, in
which case dividends on such shares shall begin to accrue from the date of issue
of such shares, or unless the date of issue is a Quarterly Dividend Payment Date
or is a date after the record date for the determination of holders of shares of
Series A Junior Participating Preferred Stock entitled to receive a quarterly
dividend and before such Quarterly Dividend Payment Date in either of which
events such dividends shall begin to accrue and be cumulative from such
Quarterly Dividend Payment Date. Accrued but unpaid dividends shall not bear
interest. Dividends paid on the shares of Series A Junior Participating
Preferred Stock in an amount less than the total amount of such dividends at the
time accrued and payable on such 



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shares shall be allocated pro rata on a share-by-share basis among all such
shares at the time outstanding. The Board of Directors may fix a record date for
the determination of holders of shares of Series A Junior Participating
Preferred Stock entitled to receive payment of a dividend or distribution
declared thereon, which record date shall be no more than 60 days prior to the
date fixed for the payment thereof.

         Section 3.        Voting Rights.  The holders of shares of Series A
Junior  Participating  Preferred Stock shall have the following voting rights:

         (A) Subject to the provision for adjustment hereinafter set forth, each
share of Series A Junior Participating Preferred Stock shall entitle the holder
thereof to 100 votes on all matters submitted to a vote of the stockholders of
the Company. In the event the Company shall at any time after the Rights
Declaration Date (i) declare any dividend on Common Stock payable in shares of
Common Stock, (ii) subdivide the outstanding Common Stock, or (iii) combine the
outstanding Common Stock into a smaller number of shares, then in each such case
the number of votes per share to which holders of shares of Series A Junior
Participating Preferred Stock were entitled immediately prior to such event
shall be adjusted by multiplying such number by a fraction the numerator of
which is the number of shares of Common Stock outstanding immediately after such
event and the denominator of which is the number of shares of Common Stock that
were outstanding immediately prior to such event.

         (B) Except as otherwise provided herein or by law, the holders of
shares of Series A Junior Participating Preferred Stock and the holders of
shares of Common Stock shall vote together as one class on all matters submitted
to a vote of stockholders of the Company.

         (C)(i) If at any time dividends on any Series A Junior Participating
         Preferred Stock shall be in arrears in an amount equal to six (6)
         quarterly dividends thereon, the occurrence of such contingency shall
         mark the beginning of a period (herein called a "default period") which
         shall extend until such time when all accrued and unpaid dividends for
         all previous quarterly dividend periods and for the current quarterly
         dividend period on all shares of Series A Junior Participating
         Preferred Stock then outstanding shall have been declared and paid or
         set apart for payment. During each default period, all holders of
         Preferred Stock (including holders of the Series A Junior Participating
         Preferred Stock) with dividends in arrears in an amount equal to six
         (6) quarterly dividends thereon, voting as a class, irrespective of
         series, shall have the right to elect two (2) Directors.

         (ii) During any default period, such voting right of the holders of
         Series A Junior Participating Preferred Stock may be exercised
         initially at a special meeting called pursuant to subparagraph (iii) of
         this Section 3(C) or at any annual meeting of stockholders, and
         thereafter at annual meetings of stockholders, provided that neither
         such voting right nor the right of the holders of any other series of
         Preferred Stock, if any, to increase, in certain cases, the authorized
         number of Directors shall be exercised unless the holders of ten
         percent (10%) in number of shares of Preferred Stock outstanding shall
         be present in person or by proxy. The absence of a quorum of the
         holders of Common Stock shall not affect the exercise by the holders of
         Preferred Stock of such voting right. 



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         At any meeting at which the holders of Preferred Stock shall exercise
         such voting right initially during an existing default period, they
         shall have the right, voting as a class, to elect Directors to fill
         such vacancies, if any, in the Board of Directors as may then exist up
         to two (2) Directors or, if such right is exercised at an annual
         meeting, to elect two (2) Directors. If the number which may be so
         elected at any special meeting does not amount to the required number,
         the holders of the Preferred Stock shall have the right to make such
         increase in the number of Directors as shall be necessary to permit the
         election by them of the required number. After the holders of the
         Preferred Stock shall have exercised their right to elect Directors in
         any default period and during the continuance of such period, the
         number of Directors shall not be increased or decreased except by vote
         of the holders of Preferred Stock as herein provided or pursuant to the
         rights of any equity securities ranking senior to or pari passu with
         the Series A Junior Participating Preferred Stock.

         (iii) Unless the holders of Preferred Stock shall, during an existing
         default period, have previously exercised their right to elect
         Directors, the Board of Directors may order, or any stockholder or
         stockholders owning in the aggregate not less than ten percent (10%) of
         the total number of shares of Preferred Stock outstanding, irrespective
         of series, may request, the calling of a special meeting of the holders
         of Preferred Stock, which meeting shall thereupon be called by the
         Chairman of the Board or the President and Chief Executive Officer of
         the Company. Notice of such meeting and of any annual meeting at which
         holders of Preferred Stock are entitled to vote pursuant to this
         paragraph (C)(iii) shall be given to each holder of record of Preferred
         Stock by mailing a copy of such notice to him at his last address as
         the same appears on the books of the Company. Such meeting shall be
         called for a time not earlier than 10 days and not later than 60 days
         after such order or request or in default of the calling of such
         meeting within 60 days after such order or request, such meeting may be
         called on similar notice by any stockholder or stockholders owning in
         the aggregate not less than ten percent (10%) of the total number of
         shares of Preferred Stock outstanding. Notwithstanding the provisions
         of this paragraph (C)(iii), no such special meeting shall be called
         during the period within 60 days immediately preceding the date fixed
         for the next annual meeting of the stockholders.

         (iv) In any default period, the holders of Common Stock, and other
         classes of stock of the Company if applicable, shall continue to be
         entitled to elect the whole number of Directors until the holders of
         Preferred Stock shall have exercised their right to elect two (2)
         Directors voting as a class, after the exercise of which right (x) the
         Directors so elected by the holders of Preferred Stock shall continue
         in office until their successors shall have been elected by such
         holders or until the expiration of the default period, and (y) any
         vacancy in the Board of Directors may (except as provided in paragraph
         (C)(ii) of this Section 3) be filled by vote of a majority of the
         remaining Directors theretofore elected by the holders of the class of
         stock which elected the Director whose office shall become vacant.
         References in this paragraph (C) to Directors elected by the holders of
         a particular class of stock shall include Directors elected by such
         Directors to fill vacancies as provided in clause (y) of the foregoing
         sentence.


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         (v) Immediately upon the expiration of a default period, (x) the right
         of the holders of Preferred Stock as a class to elect Directors shall
         cease, (y) the term of any Directors elected by the holders of
         Preferred Stock as a class shall terminate, and (z) the number of
         Directors shall be such number as may be provided for in the Restated
         Certificate of Incorporation or By-laws irrespective of any increase
         made pursuant to the provisions of paragraph (C)(ii) of this Section 3
         (such number being subject, however, to change thereafter in any manner
         provided by law or in the Restated Certificate of Incorporation or
         By-laws). Any vacancies in the Board of Directors effected by the
         provisions of clauses (y) and (z) in the preceding sentence may be
         filled by a majority of the remaining Directors.

         (D) Except as set forth herein, holders of Series A Junior
Participating Preferred Stock shall have no special voting rights and their
consent shall not be required (except to the extent they are entitled to vote
with holders of Common Stock as set forth herein) for taking any corporate
action.

         Section 4.        Certain Restrictions.

         (A) Whenever quarterly dividends or other dividends or distributions
payable on the Series A Junior Participating Preferred Stock as provided in
Section 2 are in arrears, thereafter and until all accrued and unpaid dividends
and distributions, whether or not declared, on shares of Series A Junior
Participating Preferred Stock outstanding shall have been paid in full, the
Company shall not:

         (i) Declare or pay dividends on, make any other distributions on, or
         redeem or purchase or otherwise acquire for consideration any shares of
         stock ranking junior (either as to dividends or upon liquidation,
         dissolution or winding up) to the Series A Junior Participating
         Preferred Stock;

         (ii) Declare or pay dividends on or make any other distributions on any
         shares of stock ranking on a parity (either as to dividends or upon
         liquidation, dissolution or winding up) with the Series A Junior
         Participating Preferred Stock except dividends paid ratably on the
         Series A Junior Participating Preferred Stock and all such parity stock
         on which dividends are payable or in arrears in proportion to the total
         amounts to which the holders of all such shares are then entitled;

         (iii) Redeem or purchase or otherwise acquire for consideration shares
         of any stock ranking on a parity (either as to dividends or upon
         liquidation, dissolution or winding up) with the Series A Junior
         Participating Preferred Stock provided that the Company may at any time
         redeem, purchase or otherwise acquire shares of any such parity stock
         in exchange for shares of any stock of the Company ranking junior
         (either as to dividends or upon dissolution, liquidation or winding up)
         to the Series A Junior Participating Preferred Stock; or


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<PAGE>   13

         (iv) Purchase or otherwise acquire for consideration any shares of
         Series A Junior Participating Preferred Stock or any shares of stock
         ranking on a parity with the Series A Junior Participating Preferred
         Stock except in accordance with a purchase offer made in writing or by
         publication (as determined by the Board of Directors) to all holders of
         such shares upon such terms as the Board of Directors, after
         consideration of the respective annual dividend rates and other
         relative rights and preferences of the respective series and classes,
         shall determine in good faith will result in fair and equitable
         treatment among the respective series or classes.

         (B) The Company shall not permit any subsidiary of the Company to
purchase or otherwise acquire for consideration any shares of stock of the
Company unless the Company could, under paragraph (A) of this Section 4,
purchase or otherwise acquire such shares at such time and in such manner.

         Section 5. Reacquired Shares. Any shares of Series A Junior
Participating Preferred Stock purchased or otherwise acquired by the Company in
any manner whatsoever shall be retired and cancelled promptly after the
acquisition thereof. All such shares shall upon their cancellation become
authorized but unissued shares of Preferred Stock and may be reissued as part of
a new series of Preferred Stock to be created by resolution or resolutions of
the Board of Directors, subject to the conditions and restrictions on issuance
set forth herein.

         Section 6. Liquidation, Dissolution or Winding Up.

         (A) Upon any liquidation (voluntary or otherwise), dissolution or
winding up of the Company, no distribution shall be made to the holders of
shares of stock ranking junior (either as to dividends or upon liquidation,
dissolution or winding up) to the Series A Junior Participating Preferred Stock
unless, prior thereto, the holders of shares of Series A Junior Participating
Preferred Stock shall have received per share, the greater of 100 times $75 or
100 times the payment made per share of Common Stock, plus an amount equal to
accrued and unpaid dividends and distributions thereon, whether or not declared,
to the date of such payment (the "Series A Liquidation Preference"). Following
the payment of the full amount of the Series A Liquidation Preference, no
additional distributions shall be made to the holders of shares of Series A
Junior Participating Preferred Stock unless, prior thereto, the holders of
shares of Common Stock shall have received an amount per share (the "Common
Adjustment") equal to the quotient obtained by dividing (i) the Series A
Liquidation Preference by (ii) 100 (as appropriately adjusted as set forth in
subparagraph C below to reflect such events as stock splits, stock dividends and
recapitalizations with respect to the Common Stock) (such number in clause (ii),
the "Adjustment Number"). Following the payment of the full amount of the Series
A Liquidation Preference and the Common Adjustment in respect of all outstanding
shares of Series A Junior Participating Preferred Stock and Common Stock,
respectively, holders of Series A Junior Participating Preferred Stock and
holders of shares of Common Stock shall receive their ratable and proportionate
share of the remaining assets to be distributed in the ratio of the Adjustment
Number to 1 with respect to such Preferred Stock and Common Stock, on a per
share basis, respectively.




                                      -6-
<PAGE>   14

         (B) In the event there are not sufficient assets available to permit
payment in full of the Series A Liquidation Preference and the liquidation
preferences of all other series of Preferred Stock, if any, which rank on a
parity with the Series A Junior Participating Preferred Stock then such
remaining assets shall be distributed ratably to the holders of such parity
shares in proportion to their respective liquidation preferences. In the event
there are not sufficient assets available to permit payment in full of the
Common Adjustment, then such remaining assets shall be distributed ratably to
the holders of Common Stock.

         (C) In the event the Company shall at any time after the Rights
Declaration Date (i) declare any dividend on Common Stock payable in shares of
Common Stock, (ii) subdivide the outstanding Common Stock, or (iii) combine the
outstanding Common Stock into a smaller number of shares, then in each such case
the Adjustment Number in effect immediately prior to such event shall be
adjusted by multiplying such Adjustment Number by a fraction the numerator of
which is the number of shares of Common Stock outstanding immediately after such
event and the denominator of which is the number of shares of Common Stock that
were outstanding immediately prior to such event.

         Section 7. Consolidation, Merger, etc. If the Company shall enter into
any consolidation, merger, combination or other transaction in which the shares
of Common Stock are exchanged for or changed into other stock or securities,
cash and/or any other property, then in any such event the shares of Series A
Junior Participating Preferred Stock shall at the same time be similarly
exchanged or changed in an amount per share (subject to the provision for
adjustment hereinafter set forth) equal to 100 times the aggregate amount of
stock, securities, cash and/or any other property (payable in kind), as the case
may be, into which or for which each share of Common Stock is changed or
exchanged. In the event the Company shall at any time after the Rights
Declaration Date (i) declare any dividend on Common Stock payable in shares of
Common Stock, (ii) subdivide the outstanding Common Stock, or (iii) combine the
outstanding Common Stock into a smaller number of shares, then in each such case
the amount set forth in the preceding sentence with respect to the exchange or
change of shares of Series A Junior Participating Preferred Stock shall be
adjusted by multiplying such amount by a fraction the numerator of which is the
number of shares of Common Stock outstanding immediately after such event and
the denominator of which is the number of shares of Common Stock that are
outstanding immediately prior to such event.

         Section 8. Redemption.  The shares of Series A Junior Participating
Preferred  Stock shall not be redeemable.

         Section 9. Ranking. The Series A Junior Participating Preferred Stock
shall rank junior to all other series of the Company's Preferred Stock as to the
payment of dividends and the distribution of assets, unless the terms of any
such series shall provide otherwise.

         Section 10. Fractional Shares. Series A Junior Participating Preferred
Stock may be issued in fractions of a share which shall entitle the holder, in
proportion to such holder's fractional shares, to exercise voting rights,
receive dividends, participate in distributions and to have the benefit of all
other rights of holders of Series A Junior Participating Preferred Stock.


                                      -7-
<PAGE>   15


         IN WITNESS WHEREOF, I have executed and subscribed this Certificate and
do affirm the foregoing as true under penalties of perjury this 7th day of July,
1992.


                                         By:    /s/ Britton White, Jr.
                                            --------------------------------
                                                    Britton White, Jr.
                                                  Senior Vice President
                                                    and General Counsel


Attest:


      /s/ Eldon J. Mitrisin
------------------------------------
        Assistant Secretary





                                      -8-
<PAGE>   16

                            CERTIFICATE OF AMENDMENT
                                       OF
                      RESTATED CERTIFICATE OF INCORPORATION
                                       OF
                           EL PASO NATURAL GAS COMPANY

         El Paso Natural Gas Company (the "Company"), a corporation organized
and existing under and by virtue of the General Corporation Law of the State of
Delaware,

DOES HEREBY CERTIFY:

         FIRST: That at a meeting of the Board of Directors of the Company,
resolutions were adopted setting forth a proposed amendment to the Restated
Certificate of Incorporation, as amended, declaring such amendment to be
advisable and directing that the amendment be considered at a special meeting of
stockholders of this Company. The resolution setting forth the proposed
amendment is as follows:

                  NOW, THEREFORE, BE IT RESOLVED that this Board of Directors
         hereby approves an amendment to the Restated Charter of this Company by
         deleting in its entirety the first sentence of Article 4 thereof, and
         by inserting in lieu thereof the provision set forth below so that, as
         so amended, the first sentence of said Article 4 shall read in its
         entirety as follows:

                           "The total number of authorized shares of all classes
                  of stock of this corporation shall consist of 275,000,000
                  shares of common stock having a par value of $3.00 per share
                  and 25,000,000 shares of preferred stock having a par value of
                  $0.01 per share."

         SECOND: That thereafter, pursuant to the resolution of its Board of
Directors, a special meeting of stockholders of this Company was duly called and
held, upon notice in accordance with Section 222 of the General Corporation Law
of the State of Delaware (the "DGCL"), at which meeting the holders of a
majority of the outstanding stock entitled to vote thereon, as required by the
DGCL and the Restated Certificate of Incorporation, as amended, voted in favor
of the amendment.

         THIRD: That said amendment was duly adopted in accordance with the
provisions of Section 242 of the DGCL.



<PAGE>   17

         IN WITNESS WHEREOF, said El Paso Natural Gas Company has caused this
Certificate to be signed by H. Brent Austin, its Executive Vice President and
Chief Financial Officer, and attested by David L. Siddall, its Corporate
Secretary, this 2nd day of March 1998.



                                          EL PASO NATURAL GAS COMPANY



                                          By: /s/ H. BRENT AUSTIN
                                             -------------------------------
                                                     H. Brent Austin
                                               Executive Vice President and
                                                 Chief Financial Officer

Attest:


/s/ DAVID L. SIDDALL
--------------------------------
       David L. Siddall
     Corporate Secretary




                                       -2-

<PAGE>   18

                             CERTIFICATE OF INCREASE

                                       OF

                           AUTHORIZED NUMBER OF SHARES

                                       OF

                  SERIES A JUNIOR PARTICIPATING PREFERRED STOCK

                                       OF

                           EL PASO NATURAL GAS COMPANY

           (Pursuant to Section 151 of the General Corporation Law of
                             the State of Delaware)

         El Paso Natural Gas Company, a corporation organized and existing under
the General Corporation Law of the State of Delaware, (the "Corporation"),

         DOES HEREBY CERTIFY:

         That the Restated Certificate of Incorporation of the Corporation was
filed in the office of the Secretary of State of Delaware on January 23, 1992,
and a Certificate of Designation, Preferences and Rights of Series A Junior
Participating Preferred Stock, was filed in said office of the Secretary of
State on July 7, 1992.

         That the Board of Directors of the Corporation at a meeting held on
January 21, 1998, duly adopted a resolution authorizing and directing an
increase in the authorized number of shares of Series A Junior Participating
Preferred Stock of the Corporation, from 1,000,000 to 1,375,000 shares, all in
accordance with the provisions of Section 151 of the General Corporation Law of
the State of Delaware.



<PAGE>   19

         IN WITNESS WHEREOF, said El Paso Natural Gas Company has caused this
Certificate to be signed by H. Brent Austin, its Executive Vice President and
Chief Financial Officer, and attested by David L. Siddall, its Corporate
Secretary, this 29th day of April 1998.



                                        EL PASO NATURAL GAS COMPANY



                                        By: /s/  H. BRENT AUSTIN
                                           --------------------------------
                                                   H. Brent Austin
                                            Executive Vice President and
                                               Chief Financial Officer

Attest:


/s/ DAVID L. SIDDALL
----------------------------------
         David L. Siddall
        Corporate Secretary




                                      -2-