<PAGE>   1
                                                                    EXHIBIT 4(l)

                              DECLARATION OF TRUST
                                       OF
                       ANADARKO PETROLEUM CAPITAL TRUST I


         THIS DECLARATION OF TRUST is made as of February 9, 2001 (this
"Declaration"), by and among Anadarko Petroleum Corporation, a Delaware
corporation, as sponsor (the "Sponsor"), Albert L. Richey, R. W. Tonnesen,
Suzanne Suter and The Bank of New York (Delaware), not in their individual
capacities but solely as trustees (the "Trustees"). The Sponsor and the Trustees
hereby agree as follows:

         1. The trust created hereby shall be known as "Anadarko Petroleum
Capital Trust I" (the "Trust"), in which name the Trustees or the Sponsor, to
the extent provided herein, may conduct the business of the Trust, make and
execute contracts, and sue and be sued.

         2. The Sponsor hereby assigns, transfers, conveys and sets over to the
Trust the sum of $10. Such amount shall constitute the initial trust estate. It
is the intention of the parties hereto that the Trust created hereby constitutes
a business trust under Chapter 38 of Title 12 of the Delaware Code, 12 Del. C.,
Section 3801, et seq. (the "Business Trust Act"), and that this document
constitutes the governing instrument of the Trust. The Trustees are hereby
authorized and directed to execute and file a certificate of trust with the
Delaware Secretary of State in such form as the Trustees may approve.

         3. The Sponsor and the Trustees will enter into an amended and restated
Trust Agreement or Declaration satisfactory to each such party to provide for
the contemplated operation of the Trust created hereby and the issuance of the
Preferred Securities and Common Securities referred to therein. Prior to the
execution and delivery of such amended and restated Trust Agreement or
Declaration, the Trustees shall not have any duty or obligation hereunder or
with respect of the trust estate, except as otherwise required by applicable law
or as may be necessary to obtain prior to such execution and delivery any
licenses, consents or approvals required by applicable law or otherwise.
Notwithstanding the foregoing, the Trustees may take all actions deemed proper
as are necessary to effect the transactions contemplated herein.

         4. The Sponsor is hereby authorized, in its sole discretion, (i) to
file with the Securities and Exchange Commission (the "Commission") and to
execute, in the case of the 1933 Act Registration Statement and 1934 Act
Registration Statement (as herein defined), on behalf of the Trust, (a) the 1933
Act Registration Statement, including pre-effective or post-effective amendments
to such Registration Statement, relating to the registration under the
Securities Act of 1993, as amended (the "1993 Act"), of the Preferred Securities
of the Trust, (b) any preliminary prospectus or prospectus or supplement thereto
relating to the Preferred Securities required to be filed under the 1933 Act,
and (c) if required, a Registration Statement on Form 8-A or other appropriate
form (the "1934 Act Registration Statement") (including all pre-effective and
post-effective amendments thereto) relating to the registration of the Preferred
Securities of the Trust under the Securities Exchange Act of 1934, as amended;
(ii) to file with the New York Stock Exchange or any other exchange
(collectively, the "Exchange") and execute on behalf of the Trust a listing
application and all other applications, statements, certificates,


<PAGE>   2
agreements and other instruments as shall be necessary or desirable to cause the
Preferred Securities to be listed on the Exchange; (iii) to file and execute on
behalf of the Trust such applications, reports, surety bonds, irrevocable
consents, appointments of attorney for service of process and other papers and
documents as shall be necessary or desirable to register the Preferred
Securities under the securities or "Blue Sky" laws of such jurisdictions as the
Sponsor, on behalf of the Trust, may deem necessary or desirable; (iv) to
execute, deliver and perform on behalf of the Trust, an underwriting agreement
with the Sponsor and the underwriter or underwriters of the Preferred Securities
of the Trust; (v) to execute, deliver and perform a depository agreement with
the initial clearing agency, relating to the Preferred Securities; and (vi) to
apply for and obtain a tax identification number for the Trust.

         In the event that any filing referred to in this Section 4 is required
by the rules and regulations of the Commission, PORTAL or state securities or
Blue Sky laws to be executed on behalf of the Trust by the Trustees, the
Trustees, in their capacities as trustees of the Trust, are hereby authorized
and directed to join in any such filing and to execute on behalf of the Trust
any and all of the foregoing, it being understood that H. Brent Austin, Wayne
Allred, Jeffrey I. Beason and The Bank of New York (Delaware), in their capacity
as trustees of the Trust, shall not be required to join in any such filing or
execute on behalf of the Trust any such document unless required by the rules
and regulations of the Commissions, PORTAL or state securities or Blue Sky laws.
In connection with all of the foregoing, the Sponsor hereby constitutes and
appoints H. Brent Austin, as its true and lawful attorney-in-fact and agent,
with full power of substitution and resubstitution for the Sponsor or in the
Sponsor's name, place and stead, in any and all capacities, to sign any and all
amendments (including all pre-effective and post-effective amendments) to the
1933 Act Registration Statement and any 1934 Act Registration Statement and to
file the same, with all exhibits thereto, and any other documents in connection
therewith, with the Commission, granting unto said attorney-in-fact and agent
full power and authority to do and perform each and every act and thing
requisite and necessary to be done in connection therewith, as fully to all
intents and purposes as the Sponsor might or could do in person, hereby
ratifying and confirming all that said attorney-in-fact and agent or his
respective substitute or substitutes, shall do or cause to be done by virtue
hereof.

         5. This Declaration may be executed in one or more counterparts.

         6. The number of trustees of the Trust initially shall be four (4) and
thereafter the number of trustees of the Trust shall be such number as shall be
fixed from time to time by a written instrument signed by the Sponsor which may
increase or decrease the number of trustees of the Trust; provided, however,
that the number of trustees shall in no event be less than two (2); provided,
further, that to the extent required by the Business Trust Act, one trustee of
the Trust shall either be a natural person who is a resident of the State of
Delaware or, if not a natural person, an entity which has its principal place of
business in the State of Delaware. Subject to the foregoing, the Sponsor is
entitled to appoint or remove without cause any trustee of the Trust at any
time. Any trustee of the Trust may resign upon thirty (30) days' prior notice to
the Sponsor.

         7. This Declaration shall be governed by, and construed in accordance
with, the laws of the State of Delaware.
<PAGE>   3

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



                                   By: /s/ Albert L. Richey
                                      ------------------------------------------
                                       Albert L. Richey
                                       as Administrative Trustee


                                   By: /s/ R. W. Tonnesen
                                      ------------------------------------------
                                       R. W. Tonnesen
                                       as Administrative Trustee


                                   By: /s/ Suzanne Suter
                                      ------------------------------------------
                                       Suzanne Suter
                                       as Administrative Trustee


                                   THE BANK OF NEW YORK (DELAWARE)
                                   not in its individual capacity but solely
                                   as a trustee of the Trust


                                   By: /s/ Michael Santino
                                      ------------------------------------------
                                       Name: Michael Santino, SVP
                                       Title:


                                   ANADARKO PETROLEUM CORPORATION, as
                                   Sponsor


                                   By: /s/ Suzanne Suter
                                      ------------------------------------------
                                       Name: Suzanne Suter
                                       Title: Corporate Secretary