<Page>
EXHIBIT 4.8
DECLARATION OF TRUST, dated as of August 29, 2002 between Marathon Oil
Corporation, a Delaware corporation, as Sponsor (the "Sponsor"), and The Bank of
New York, as trustee (the "Property Trustee"), The Bank of New York (Delaware),
as trustee (the "Delaware Trustee"), and P.C. Reinbolt, as trustee (the "Regular
Trustee") (the Property Trustee, the Delaware Trustee and the Regular Trustee,
collectively the "Trustees"). The Sponsor and the Trustees hereby agree as
follows:
1. The Delaware business trust created hereby shall be known as "Marathon
Financing 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. The Trust hereby acknowledges receipt of such amount from
the Sponsor, which amount shall constitute the initial trust estate. It is the
intention of the parties hereto that the Trust created hereby constitute a
business trust under Chapter 38 of Title 12 of the Delaware Code, 12 DEL. CODE
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
Secretary of State of the State of Delaware in substantially the form attached
hereto in accordance with the provisions of the Business Trust Act. The Trust is
hereby established by the Sponsor and the Trustees for the purposes of (i)
issuing preferred securities representing undivided beneficial interests in the
assets of the Trust ("Preferred Securities") in exchange for cash and investing
the proceeds thereof in debt securities of the Sponsor, (ii) issuing and selling
common securities representing undivided beneficial interests in the assets of
the Trust ("Common Securities") to the Sponsor in exchange for cash and
investing the proceeds thereof in additional debt securities of the Sponsor and
(iii) engaging in such other activities as are necessary or incidental thereto.
3. The Sponsor and the Trustees will enter into an Amended and Restated
Declaration of Trust, satisfactory to each such party and substantially in the
form included as an exhibit to the Securities Act Registration Statement
referred to below, 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 Declaration of Trust, the Trustees shall not have any duty
or obligation hereunder or with respect to 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.
4. The Sponsor, as the sponsor of the Trust, is hereby authorized (i) to
prepare and file with the Securities and Exchange Commission (the "Commission")
and execute, in each case on behalf of the Trust, (a) a Registration Statement
on Form S-3 or on such other form or forms as may be appropriate, including
without limitation any registration statement of the type contemplated by Rule
462(b) of the Securities Act of 1933, as amended (the "Securities Act") (any
such registration statement, whether on Form S-3, another form or under Rule
462(b) being referred to herein as the "Securities Act Registration Statement"),
including any pre-effective or post-effective amendments to such Registration
Statement (including any
<Page>
preliminary prospectus, prospectus or prospectus supplement, and the exhibits
contained therein), relating to the registration under the Securities Act of the
Preferred Securities and certain other securities of the Sponsor and (b) if the
Sponsor shall deem it desirable, a Registration Statement on Form 8-A (the
"Exchange Act Registration Statement"), including all pre-effective and
post-effective amendments thereto, relating to the registration of the Preferred
Securities under Section 12 of the Securities Exchange Act of 1934, as amended;
(ii) if the Sponsor shall deem it desirable, to prepare and file with New York
Stock Exchange, Inc. or any other automated quotation system, exchange or
over-the-counter market (collectively, the "Exchanges") and execute on behalf of
the Trust a listing application or applications and all other applications,
statements, certificates, agreements and other instruments as shall be necessary
or desirable to cause the Preferred Securities to be listed on any Exchange;
(iii) to prepare and 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 the Sponsor, on behalf of
the Trust, may deem 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 negotiate the
terms of and execute on behalf of the Trust an underwriting or other purchase
agreement among the Trust, the Sponsor and any underwriter(s), dealer(s) or
agent(s) relating to the Preferred Securities, as the Sponsor, on behalf of the
Trust, may deem necessary or desirable; and (v) to execute and deliver on behalf
of the Trust letters or documents to, or instruments for filing with, a
depository relating to the Preferred Securities. In the event that any filing
referred to in clauses (i)-(iii) above is required by the rules and regulations
of the Commission, any Exchange, the National Association of Securities Dealers,
Inc. or state securities or blue sky laws, to be executed on behalf of the Trust
by a Trustee, any natural person appointed pursuant to Section 6 hereof, in his
or her capacity as trustee of the Trust, and the Sponsor are hereby authorized
to join in any such filing and to execute on behalf of the Trust any and all of
the foregoing.
5. This Declaration of Trust may be executed in one or more counterparts.
6. The number of Trustees initially shall be three (3) and thereafter the
number of Trustees shall be such number as shall be fixed from time to time by a
written instrument signed by the Sponsor that may increase or decrease the
number of Trustees; PROVIDED, HOWEVER, that the number of Trustees shall in no
event be less than three (3); and PROVIDED, FURTHER that to the extent required
by the Business Trust Act, one Trustee shall either be a natural person who is a
resident of the State of Delaware or, if not a natural person, an entity that
has its principal place of business in the State of Delaware and meets other
requirements imposed by applicable law. Subject to the foregoing, the Sponsor is
entitled to appoint or remove without cause any Trustee at any time. Any Trustee
may resign upon thirty days' prior notice to the Sponsor.
7. The Trust may be dissolved and terminated at the election of the
Sponsor.
8. This Declaration of Trust shall be governed by, and construed in
accordance with, the laws of the State of Delaware (without regard to conflict
of laws principles).
2
<Page>
9. To the fullest extent permitted by applicable law, the Sponsor shall
indemnify and hold harmless any Trustee, any affiliate of any Trustee, any
paying agent, any officer, director, shareholder, member, partner, employee,
representative or agent of any Trustee or paying agent, or any employee or agent
of the Trust or of any of its affiliates, including but not limited to any
officer or director of the Sponsor (an "Indemnified Person") from and against
any loss, liability, expense, damage or claim incurred by such Indemnified
Person arising out of or in connection with the acceptance or administration of
the trust or trusts hereunder or by reason of any act or omission performed or
omitted by such Indemnified Person in good faith on behalf of the Trust and in a
manner such Indemnified Person reasonably believed to be within the scope of
authority conferred on such Indemnified Person by this Declaration of Trust,
except that no Indemnified Person shall be entitled to be indemnified in respect
of any loss, liability, expense, damage or claim incurred by such Indemnified
Person by reason of gross negligence (or, in the case of the Property Trustee,
negligence) or willful misconduct with respect to such acts or omissions.
3
<Page>
IN WITNESS WHEREOF, the parties hereto have caused this Declaration of
Trust to be duly executed as of the day and year first above written.
MARATHON OIL CORPORATION,
as Sponsor
By: /s/ JOHN T. MILLS
-----------------------------------
John T. Mills,
Chief Financial Officer
THE BANK OF NEW YORK,
as Property Trustee
By: /s/ REMO J. REALE
-----------------------------------
Name: Remo J. Reale
Title: Vice President
THE BANK OF NEW YORK (DELAWARE),
as Delaware Trustee
By: /s/ JAMES LONGSHAW
-----------------------------------
Name: James Longshaw
Title: Senior Vice President
P.C. REINBOLT,
as Regular Trustee
/s/ P.C. REINBOLT
---------------------------------------