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                                                                Exhibit (10)(aa)

                            THE LUBRIZOL CORPORATION
                      2005 EXCESS DEFINED CONTRIBUTION PLAN

      The Lubrizol Corporation hereby establishes, effective as of January 1,
2005, The Lubrizol Corporation 2005 Excess Defined Contribution Plan (the
"Plan") for the purpose of supplementing the benefits of certain employees, as
permitted by Section 3(36) of the Employee Retirement Income Security Act of
1974.

                                    ARTICLE I

                                   DEFINITIONS

      1.1 Definitions. For the purposes hereof, the following words and phrases
shall have the meanings indicated, unless a different meaning is plainly
required by the context:

            (a) Beneficiary. The term "Beneficiary" shall mean the person or
      persons who shall be designated by a Participant to receive distribution
      of such Participant's interest under the Plan in the event such
      Participant dies before full distribution of his interest.

            (b) Code. The term "Code" shall mean the Internal Revenue Code as
      amended from time to time. Reference to a section of the Code shall
      include such section and any comparable section or sections of any future
      legislation that amends, supplements, or supersedes such section.

            (c) Company. The term "Company" shall mean The Lubrizol Corporation,
      an Ohio corporation, its corporate successors and the surviving
      corporation resulting from any merger of The Lubrizol Corporation with any
      other corporation or corporations, and any subsidiaries of The Lubrizol
      Corporation which adopt the Plan.

            (d) Executive Council Deferred Compensation Plan. The term
      "Executive Council Deferred Compensation Plan" shall mean The Lubrizol
      Corporation 2005 Executive Council Deferred Compensation Plan, as shall be
      in effect on the date of the Participant's retirement, death, or other
      termination of employment.

            (e) Fund. The term "Fund" shall mean each separate investment fund
      established and maintained under the Trust Agreement.

            (f) Lubrizol Deferred Compensation Plan. The term "Lubrizol Deferred
      Compensation Plan" shall mean The Lubrizol Corporation 2005 Deferred
      Compensation Plan for Officers, as shall be in effect on the date of the
      Participant's retirement, death, or other termination of employment.

            (g) Participant. The term "Participant" shall mean any person
      employed by the Company who is listed on Appendix A attached hereto, or
      who is designated by the Board of Directors as an officer for the purposes
      of Section 16 of the Securities Exchange Act of 1934, or whose benefits
      under the Profit-Sharing Plan are limited by the application of Section
      401(a)(17) of the Internal Revenue Code of 1986, as amended.

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            (h) Plan. The term "Plan" shall mean the excess defined contribution
      retirement plan as set forth herein, together with all amendments hereto,
      which Plan shall be called "The Lubrizol Corporation Excess Defined
      Contribution Plan."

            (i) Plan Year. The term "Plan Year" shall mean the calendar year.

            (j) Profit-Sharing Plan. The term "Profit-Sharing Plan" shall mean
      The Lubrizol Corporation Employees' Profit-Sharing Plan and Savings Plan
      as the same shall be in effect on the date of a Participant's retirement,
      death, or other termination of employment.

            (k) Supplemental Company Contributions. The term "Supplemental
      Company Contributions" shall mean the contributions made by the Company
      under the Plan in accordance with the provisions of Section 2.2.

            (l) Trust Agreement. The term "Trust Agreement" shall mean The
      Lubrizol Corporation Excess Defined Contribution Plan Trust Agreement.

            (m) Trust Assets. The term "Trust Assets" shall mean all property
      held by the Trustee pursuant to the Trust Agreement.

            (n) Trustee. The term "Trustee" shall mean the trustee of The
      Lubrizol Corporation Excess Defined Contribution Trust.

            (o) Valuation Date. The term "Valuation Date" shall mean the last
      day of each Plan Year and any other date as may be agreed upon by the
      Company and the Trustee.

            (p) Separate Accounts. The term "Separate Accounts" shall mean each
      account established on behalf of a Participant under the Plan and credited
      with Supplemental Company Contributions in accordance with the provisions
      of Section 2.3.

      1.2 Additional Definitions. All other words and phrases used herein shall
have the meanings given them in the Profit-Sharing Plan, unless a different
meaning is clearly required by the context.

                                   ARTICLE II

                           SUPPLEMENTAL CONTRIBUTIONS

      2.1 Eligibility. A Participant whose benefits under the Profit-Sharing
Plan are limited with respect to any Plan Year by Section 401(a)(17) or 415 of
the Code, or who participated in the Lubrizol Deferred Compensation Plan or the
Executive Council Deferred Compensation Plan, shall be eligible to have
contributions made with respect to him under the Plan in accordance with the
provisions of this Article II.

      2.2 Supplemental Company Contributions. In the event that Company
contributions under the Lubrizol Profit-Sharing Plan with respect to a
Participant are limited for any Plan Year due to the provisions of Section
401(a)(17) or 415 of the Code, or due to the Participant's participation in the
Lubrizol Deferred Compensation Plan or the Executive Council Deferred
Compensation Plan, the amounts by which such contributions are limited shall be
credited

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under the Plan by the Company and shall be designated as Supplemental Company
Contributions.

      2.3 Allocation of Contributions. Supplemental Company Contributions shall
be allocated among the Separate Accounts of the Participants on whose behalf
such contributions are made.

      2.4 Administration of Separate Accounts. Each Separate Account to which
contributions under Sections 2.2 and 2.3 are credited and allocated shall be
credited monthly with the net monthly increase experienced by the General Fund
of the Lubrizol Profit-Sharing Plan.

                                   ARTICLE III

                                  DISTRIBUTION

      3.1 Vesting. Each Participant, shall be vested in the value of his
Separate Accounts under this Plan as determined in accordance with the vesting
provisions of the Profit-Sharing Plan.

      3.2 Distribution.

            (a) Each Participant who separates from service with the Company and
      its related corporations shall receive payment of the balance in his
      Separate Account in the standard form of payment of a single lump-sum
      payment payable the later of six months following the separation from
      service or 30 days following the calendar year in which Participant
      separated from service.

            (b) At least 12 months prior to the distribution date specified in
      paragraph (a) Participants may instead elect to receive the balance of his
      Separate Account in annual installments of up to ten payments, the first
      of which shall be paid five years following the original distribution date
      specified in paragraph (a), and subsequent installments of which shall be
      paid on the anniversary date of the payment of the first installment. Such
      installments shall be determined by dividing the value of the
      Participant's Separate Account by the number of installments to be.

      3.3 Distribution in the Event of Death. In the event of the death of a
Participant prior to distribution in full of his interest under the Plan, his
Beneficiary shall receive distribution of such interest. In the event of death
of a Participant prior to making an election for benefits, such Beneficiary
shall receive distribution of such interest as soon as practicable after such
Participant's death in the form elected by such Beneficiary pursuant to Section
3.2. The Beneficiary under this Section 3.3 shall be the person designated as
the Participant's beneficiary under the Profit-Sharing Plan. If no Beneficiary
survives such Participant or if no Beneficiary has been designated by such
Participant, the estate of such Participant shall be the Beneficiary and receive
distribution thereof. If any Beneficiary dies after becoming entitled to receive
distribution hereunder and before such distribution is made in full, and if no
other person or persons have been designated to receive the balance of such
distribution upon the happening of such contingency, the estate of such deceased
Beneficiary shall become the Beneficiary as to such balance.

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                                   ARTICLE IV

                                 ADMINISTRATION

      4.1 Authority of the Company. The Company shall be responsible for the
general administration of the Plan, for carrying out the provisions hereof, and
for making, or causing the Trust to make, any required supplemental benefit
payments. The Company shall have all such powers as may be necessary to carry
out the provisions of the Plan, including the power to determine all questions
relating to eligibility for and the amount of any supplemental pension benefit
and all questions pertaining to claims for benefits and procedures for claim
review; to resolve all other questions arising under the Plan, including any
questions of construction; and to take such further action as the Company shall
deem advisable in the administration of the Plan. The Company may delegate any
of its powers, authorities, or responsibilities for the operation and
administration of the Plan to any person or committee so designated in writing
by it and may employ such attorneys, agents, and accountants as it may deem
necessary or advisable to assist it in carrying out its duties hereunder. The
actions taken and the decisions made by the Company hereunder shall be final and
binding upon all interested parties.

      4.2 Claims Review Procedure. The Company shall notify the person who files
a claim for benefits (hereinafter referred to as the "Claimant") of the Plan's
adverse benefit determination within a reasonable period of time, but not later
than 90 days after the receipt of the claim by the Plan, unless the Company
determines that special circumstances require an extension of time for
processing the claim. If the Company determines that special circumstances
require an extension of time for processing is required, written notice of the
extension shall be furnished to the Claimant prior to the termination of the
initial 90-day period. In no event shall such extension exceed a period of 90
days from the end of such initial period. The extension notice shall indicate
the special circumstances requiring an extension of time and the date by which
the Plan expects to render the benefit determination. Whenever the Company
decides for whatever reason to deny, whether in whole or in part, a claim for
benefits filed by any Claimant, the Company shall transmit to the Claimant a
written notice of the Company's decision, which shall be written in a manner
calculated to be understood by the Claimant and contain a statement of the
specific reasons for the denial of the claim, reference to the specific Plan
provisions on which the determination was based, a description of any additional
material or information necessary for the Claimant to perfect the claim and an
explanation of why such material or information is necessary, a description of
the Plan's review procedures and the time limits applicable to such procedures,
include a statement of the Claimant's right to bring civil action under Section
502(a) ERISA following an adverse benefit determination on review. Within 60
days of the date on which the Claimant receives such notice, he or his
authorized representative may request that the claim denial be reviewed by
filing with the Company a written request therefor, which request shall contain
the following information:

            (a) the date on which the Claimant's request was filed with the
            Company; provided, however, that the date on which the Claimant's
            request for review was in fact filed with the Company shall control
            in the event that the date of the actual filing is later than the
            date stated by the Claimant pursuant to this paragraph (a);

            (b) the specific portions of the denial of his claim which the
            Claimant requests the Company to review;

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            (c) a statement by the Claimant setting forth the basis upon which
            he believes the Company should reverse the Company's previous denial
            of his claim for benefits and accept his claim as made; and

            (d) any written comments, documents, records and other information
            which the Claimant desires the Company to examine in its
            consideration of his position as stated pursuant to paragraph (c).

Claimant shall be provided, upon request and free of charge, reasonable access
to, and copies of, all documents, records, and other information relevant to the
Claimant's claim for benefits. The review of the claim will take into account
all comments, documents, records and other information submitted by the Claimant
relating to the claim, without regard to whether such information was submitted
or considered in the initial benefit determination. Within no later than 60 days
of the date determined pursuant to paragraph (a) of this Section 4.2, the
Company shall notify Claimant of the Plan's benefit determination, unless the
Company determines that special circumstances require an extension of time for
processing the claim. If the Company determines that an extension of time for
processing is required, written notice of the extension will be furnished to the
Claimant prior to the termination of the initial 60-day period. In no event
shall such extension exceed a period of 60 days from the end of the initial
period. The extension notice shall indicate the special circumstances requiring
an extension of time and the date by which the Plan expects to render the
determination on review. The Company shall provide the Claimant with a written
notification of the Plan's benefit determination on review, written in a manner
calculated to be understood by the Claimant, including the reasons and Plan
provisions upon which its decision was based, a statement that the Claimant is
entitled to receive, upon request and free of charge, reasonable access to, and
copies of, all documents, records and other information relevant to the
Claimant's claim for benefits, and a statement of the Claimant's right to bring
an action under Section 502(a) of ERISA.

                                    ARTICLE V

                            AMENDMENT AND TERMINATION

      The Company reserves the right to amend or terminate the Plan in whole or
in part at any time and to suspend operation of the Plan, in whole or in part,
at any time, by resolution or written action of its Board of Directors or by
action of a committee to which such authority has been delegated by the Board of
Directors; provided, however, that no amendment shall result in the forfeiture
or reduction of the interest of any Participant or person claiming under or
through any one or more of them pursuant to the Plan. Any amendment of the Plan
shall be in writing and signed by authorized individuals.

                                   ARTICLE VI

                                  MISCELLANEOUS

      6.1 Non-Alienation of Retirement Rights or Benefits. No Participant shall
encumber or dispose of his right to receive any payments hereunder, which
payments or the right thereto are expressly declared to be non-assignable and
non-transferable. If a Participant or Beneficiary attempts to assign, transfer,
alienate or encumber his right to receive any payment under the Plan or permits
the same to be subject to alienation, garnishment, attachment, execution, or

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levy of any kind, then thereafter during the life of such Participant or
Beneficiary and also during any period in which any Participant or Beneficiary
is incapable in the judgment of the Company of attending to his financial
affairs, any payments which the Company is required to make hereunder may be
made, in the discretion of the Company, directly to such Participant or
Beneficiary or to any other person for his use or benefit or that of his
dependents, if any, including any person furnishing goods or services to or for
his use or benefit or the use or benefit of his dependents, if any. Each such
payment may be made without the intervention of a guardian, the receipt of the
payee shall constitute a complete acquittance to the Company with respect
thereto, and the Company shall have no responsibility for the proper allocation
thereof.

      6.2 Plan Non-Contractual. Nothing herein contained shall be construed as a
commitment or agreement on the part of any person employed by the Company to
continue his employment with the Company, and nothing herein contained shall be
construed as a commitment on the part of the Company to continue the employment
or the annual rate of compensation of any such person for any period, and all
Participants shall remain subject to discharge to the same extent as if the Plan
had never been established.

      6.3 Trust. In order to provide a source of payment for its obligations
under the Plan, the Company has established The Lubrizol Corporation Excess
Defined Contribution Plan Trust.

      6.4 Interest of a Participant. Subject to the provisions of the Trust
Agreement, the obligation of the Company under the Plan to provide a Participant
or Beneficiary with supplemental retirement benefits merely constitutes the
unsecured promise of the Company to make payments as provided herein, and no
person shall have any interest in, or a lien or prior claim upon, any property
of the Company.

      6.5 Controlling Status. No Participant shall be eligible for a benefit
under the Plan unless such Participant is a Participant on the date of his
retirement, death, or other termination of employment.

      6.6 Claims of Other Persons. The provisions of the Plan shall in no event
be construed as giving any person, firm or corporation any legal or equitable
right as against the Company, its officers, employees, or directors, except any
such rights as are specifically provided for in the Plan or are hereafter
created in accordance with the terms and provisions of the Plan.

      6.7 Severability. The invalidity or unenforceability of any particular
provision of the Plan shall not affect any other provision hereof, and the Plan
shall be construed in all respects as if such invalid or unenforceable provision
were omitted herefrom.

      6.8 Governing Law. The provisions of the Plan shall be governed and
construed in accordance with the laws of the State of Ohio.

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                                   APPENDIX A
                                       TO
                            THE LUBRIZOL CORPORATION
                        EXCESS DEFINED CONTRIBUTION PLAN

<TABLE>
<CAPTION>
Participants                                       Effective Date
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<S>                                                <C>
</TABLE>