<PAGE>
           FIRST AMENDMENT TO MILLENNIUM ASSET CONTRIBUTION AGREEMENT

      This First Amendment to Millennium Asset Contribution Agreement (this
"First Amendment"), dated as of May 15, 1998, is entered into by and among
Millennium Petrochemicals Inc., a Virginia corporation (the "Contributor"),
Millennium Petrochemicals LP LLC, a Delaware limited liability company (the
"Contributing Partner") and Equistar Chemicals, LP, a Delaware limited
partnership (the "Partnership").

                                    RECITALS

      A. The Contributor, the Contributing Partner and the Partnership are
parties to that certain Asset Contribution Agreement dated as of December 1,
1997 (the "1997 Asset Contribution Agreement");

      B. Pursuant to that certain Master Transaction Agreement, dated as of May
15, 1998, by and among Millennium Chemicals Inc., the Partnership, Occidental
Petroleum Corporation ("OPC") and Lyondell Petrochemical Company, certain
affiliates of OPC shall become partners in the Partnership as of the date
hereof; and

      C. The Contributor, the Contributing Partner and the Partnership desire to
amend the 1997 Asset Contribution Agreement on the terms set forth herein.

                                    AGREEMENT

      NOW THEREFORE, in consideration of the premises and of the mutual
covenants of the parties hereto, it is hereby agreed that the 1997 Asset
Contribution Agreement is amended as follows:

      A. Capitalized terms used herein and not otherwise defined herein shall
have the meanings given such terms in the 1997 Asset Contribution Agreement.

      B. The following definition shall be added to Section 1 of the 1997 Asset
Contribution Agreement:

      "1998 MTA" shall mean that certain Master Transaction Agreement, dated as
of May 15, 1998, by and among Millennium Chemicals Inc., the Partnership,
Occidental Petroleum Corporation and Lyondell Petrochemical Company.

      C. The definition of "Third Party Claim" as set forth in Section 1 of the
1997 Asset Contribution Agreement shall be amended and restated as follows:

      "Third Party Claim" means any allegation, claim, civil or criminal action,
proceeding, charge or prosecution brought by a Person other than a Contributor,
any Affiliate thereof, the Partnership,







<PAGE>

any member of the Millennium Group (as defined in the 1998 MTA), any member of
the Lyondell Group (as defined in the 1998 MTA) or any member of the Occidental
Group (as defined in the 1998 MTA).

      D. Subsection 6.2(a)(i) of the 1997 Asset Contribution Agreement shall be
amended and restated as follows:

            (i) Any misrepresentation in or breach of the representations and
      warranties of the Contributor or any of its Affiliates in this Agreement,
      the Assignment and Assumption Agreements, the Master Intellectual Property
      Agreement, or the Master Transaction Agreement, provided that any
      Liability arising out of, in connection with or relating to any breach of
      the warranties in any Assignment and Assumption Agreement that is not a
      breach of the warranties in this Agreement shall not be indemnified
      against pursuant to this Section 6;

      E. Subsection 6.2(b) of the 1997 Asset Contribution Agreement shall be
amended and restated as follows:

            (b) NOTWITHSTANDING ANY OTHER PROVISION OF THIS AGREEMENT, TO THE
      FULLEST EXTENT PERMITTED BY LAW, NEITHER THE CONTRIBUTOR NOR ANY OF ITS
      AGENTS, EMPLOYEES, REPRESENTATIVES OR AFFILIATES SHALL BE LIABLE FOR
      CONSEQUENTIAL, INCIDENTAL, INDIRECT OR PUNITIVE DAMAGES IN CONNECTION WITH
      DIRECT CLAIMS BY AN INDEMNIFIED PARTY (I.E., A CLAIM BY AN INDEMNIFIED
      PARTY THAT DOES NOT SEEK REIMBURSEMENT FOR A THIRD PARTY CLAIM PAID OR
      PAYABLE BY SUCH INDEMNIFIED PARTY) WITH RESPECT TO THEIR INDEMNIFICATION
      OBLIGATIONS UNDER THIS AGREEMENT UNLESS ANY SUCH CLAIM ARISES OUT OF THE
      FRAUDULENT ACTIONS OF THE CONTRIBUTOR. IN DETERMINING THE AMOUNT OF ANY
      LOSS, LIABILITY, OR EXPENSE FOR WHICH AN INDEMNIFIED PARTY IS ENTITLED TO
      INDEMNIFICATION UNDER THIS AGREEMENT, THE GROSS AMOUNT THEREOF WILL BE
      REDUCED (BUT NOT BELOW ZERO) BY THE NET PRESENT VALUE OF ANY CORRELATIVE
      INSURANCE PROCEEDS ACTUALLY REALIZED BY SUCH INDEMNIFIED PARTY UNDER
      POLICIES TO THE EXTENT THAT THE FUTURE PREMIUM RATE WILL NOT BE INCREASED
      BY CLAIM EXPERIENCE RELATING TO SUCH LOSS, LIABILITY OR EXPENSE.

      F. Subsection 6.2(e) of the 1997 Asset Contribution Agreement shall be
amended and restated as follows:

            (e) NOTWITHSTANDING ANY OTHER PROVISION OF THIS AGREEMENT, TO THE
      FULLEST EXTENT PERMITTED BY LAW, NEITHER THE PARTNERSHIP NOR ANY OF ITS
      AGENTS, EMPLOYEES, REPRESENTATIVES OR AFFILIATES SHALL BE LIABLE FOR
      CONSEQUENTIAL, INCIDENTAL, INDIRECT







<PAGE>

      OR PUNITIVE DAMAGES IN CONNECTION WITH DIRECT CLAIMS BY AN INDEMNIFIED
      PARTY (I.E., A CLAIM BY AN INDEMNIFIED PARTY THAT DOES NOT SEEK
      REIMBURSEMENT FOR A THIRD PARTY CLAIM PAID OR PAYABLE BY SUCH INDEMNIFIED
      PARTY) WITH RESPECT TO THEIR INDEMNIFICATION OBLIGATIONS UNDER THIS
      AGREEMENT UNLESS ANY SUCH CLAIM ARISES OUT OF THE FRAUDULENT ACTIONS OF
      THE PARTNERSHIP. IN DETERMINING THE AMOUNT OF ANY LOSS, LIABILITY, OR
      EXPENSE FOR WHICH AN INDEMNIFIED PARTY IS ENTITLED TO INDEMNIFICATION
      UNDER THIS AGREEMENT, THE GROSS AMOUNT THEREOF WILL BE REDUCED (BUT NOT
      BELOW ZERO) BY THE NET PRESENT VALUE OF ANY CORRELATIVE INSURANCE PROCEEDS
      ACTUALLY REALIZED BY SUCH INDEMNIFIED PARTY UNDER POLICIES TO THE EXTENT
      THE FUTURE PREMIUM RATE WILL NOT BE INCREASED BY CLAIM EXPERIENCE RELATING
      TO SUCH LOSS, LIABILITY OR EXPENSE.

      G. Appendix A to the 1997 Asset Contribution Agreement shall be amended
and restated in its entirety in the form attached hereto as Exhibit A.

      H. Except as amended by this First Amendment, all the terms and provisions
of the 1997 Asset Contribution Agreement shall remain in full force and effect.

                  [Remainder of Page Intentionally Left Blank]







<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed and delivered this First
Amendment as of the date first above written.

                                    MILLENNIUM PETROCHEMICALS INC.,
                                    a Virginia corporation.

                                    By: /s/ George H. Hempstead, III
                                        -----------------------------------
                                    Name:  George H. Hempstead, III
                                           --------------------------------
                                    Title: Senior Vice President
                                           --------------------------------


                                    MILLENNIUM PETROCHEMICALS LP LLC,
                                    a Delaware limited liability company.

                                    By:
                                        -----------------------------------
                                    Name:  George H. Hempstead, III
                                           --------------------------------
                                    Title: Senior Vice President
                                           --------------------------------


                                    EQUISTAR CHEMICALS, LP,
                                    a Delaware limited partnership

                                    By: /s/ Eugene R. Allspach
                                        -----------------------------------
                                    Name:  Eugene R. Allspach
                                           --------------------------------
                                    Title: President and Chief Operating Officer
                                           --------------------------------

 [Signature Page to First Amendment To Millennium Asset Contribution Agreement]







<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed and delivered this First
Amendment as of the date first above written.

                                    MILLENNIUM PETROCHEMICALS INC.,
                                    a Virginia corporation.

                                    By: /s/ George H. Hempstead, III
                                        -----------------------------------
                                    Name:  George H. Hempstead, III
                                           --------------------------------
                                    Title: Senior Vice President
                                           --------------------------------


                                    MILLENNIUM PETROCHEMICALS LP LLC,
                                    a Delaware limited liability company.

                                    By: /s/ George H. Hempstead, III
                                        -----------------------------------
                                    Name:  George H. Hempstead, III
                                           --------------------------------
                                    Title: Senior Vice President
                                           --------------------------------


                                    EQUISTAR CHEMICALS, LP,
                                    a Delaware limited partnership

                                    By:
                                        -----------------------------------
                                    Name:  Eugene R. Allspach
                                           --------------------------------
                                    Title: President and Chief Operating Officer
                                           --------------------------------

 [Signature Page to First Amendment To Millennium Asset Contribution Agreement]







<PAGE>

                                    EXHIBIT A

                                   Appendix A

                          Dispute Resolution Procedures

      (1) Binding and Exclusive Means. The dispute resolution provisions set
forth in this Appendix A shall be the binding and exclusive means to resolve all
disputes arising under this Agreement (each a "Dispute").

      (2) Standards and Criteria. In resolving any Dispute, the standards and
criteria for resolving such dispute shall, unless the Contributors and the
Partnership in their discretion jointly stipulate otherwise, be as set forth in
Appendix 1 to this Appendix A.

      (3) ADR and Binding Arbitration Procedures. If a Dispute arises, the
following procedures shall be implemented:

      (a) Any party to this Agreement may at any time invoke the dispute
resolution procedures set forth in this Appendix A as to any Dispute by
providing written notice of such action to the other party or parties to the
Dispute, who within five Business Days after such notice shall schedule a
meeting to be held in Houston, Texas between the parties. The meeting shall
occur within 10 Business Days after notice of the meeting is delivered to the
other party or parties. The meeting shall be attended by representatives of each
party having decision-making authority regarding the Dispute as well as the
dispute resolution process and who shall attempt in a commercially reasonable
manner to negotiate a resolution of the Dispute.

      (b) The representatives of the parties shall cooperate in a commercially
reasonable manner and shall explore whether techniques such as mediation,
minitrials, mock trials or other techniques of alternative dispute resolution
might be useful. In the event that a technique of alternative dispute resolution
is so agreed upon, a specific timetable and completion date for its
implementation shall also be agreed upon. The representatives will continue to
meet and discuss settlement until the date (the "Interim Decision Date") that is
the earliest to occur of the following events: (i) an agreement shall be reached
by the parties resolving the Dispute; (ii) one of the parties shall determine
and notify the other party in writing that no agreement resolving the Dispute is
likely to be reached; (iii) if a technique of alternative dispute resolution is
agreed upon, the completion date therefor shall occur without the parties having
resolved the Dispute; or (iv) if another technique of alternative dispute
resolution is not agreed upon, two full meeting days (or such other time period
as may be agreed upon) shall expire without the parties having resolved the
Dispute.







<PAGE>

      (c) If, as of the Interim Decision Date, the parties have not succeeded in
negotiating a resolution of the dispute pursuant to subsection (b), the parties
shall proceed under subsections (d), (e) and (f).

      (d) After satisfying the requirements above, such Dispute shall be
submitted to mandatory and binding arbitration at the election of any party
involved in the Dispute (the "Disputing Party"). The arbitration shall be
subject to the Federal Arbitration Act as supplemented by the conditions set
forth in this Appendix. The arbitration shall be conducted in accordance with
the Commercial Arbitration Rules of the American Arbitration Association in
effect on the date the notice of arbitration is served, other than as
specifically modified herein. In the absence of an agreement to the contrary,
the arbitration shall be held in Houston, Texas. The Arbitrator (as defined
below) will allow reasonable discovery in the forms permitted by the Federal
Rules of Civil Procedure, to the extent consistent with the purpose of the
arbitration. During the pendency of the Dispute, each party shall make available
to the Arbitrator and the other parties all books, records and other information
within its control requested by the other parties or the Arbitrator subject to
the confidentiality provisions contained herein, and provided that no such
access shall waive or preclude any objection to such production based on any
privilege recognized by law. Recognizing the express desire of the parties for
an expeditious means of dispute resolution, the Arbitrator may limit the scope
of discovery between the parties as may be reasonable under the circumstances.
In deciding the substance of the parties' claims, the laws of the State of
Delaware shall govern the construction, interpretation and effect of this
Agreement (including this Appendix) without giving effect to any conflict of law
principles. The arbitration hearing shall be commenced promptly and conducted
expeditiously, with each party involved in the Dispute being allocated an equal
amount of time for the presentation of its case. Unless otherwise agreed to by
the parties, the arbitration hearing shall be conducted on consecutive days.
Time is of the essence in the arbitration proceeding, and the Arbitrator shall
have the right and authority to issue monetary sanctions against any of the
parties if, upon a showing of good cause, that party is unreasonably delaying
the proceeding. To the fullest extent permitted by law, the arbitration
proceedings and award shall be maintained in confidence by the Arbitrator and
the parties.

      (e) The Disputing Party shall notify the American Arbitration Association
("AAA") and the other parties involved in the Dispute in writing describing in
reasonable detail the nature of the Dispute (the "Dispute Notice"). The
arbitrator (the "Arbitrator") shall be selected within 15 days of the date of
the Dispute Notice by all of the parties from the members of a panel of
arbitrators of the AAA or, if the AAA fails or refuses to provide a list of
potential arbitrators, of the Center for Public Resources and shall be
experienced in commercial arbitration. In the event that the parties are unable
to agree on the selection of the Arbitrator, the AAA shall select the
Arbitrator, using the criteria set forth in this Appendix, within 30 days of the
date of the Dispute Notice. In the event that the Arbitrator is unable to serve,
his or her replacement will be selected in the same manner as the Arbitrator to
be replaced. The Arbitrator shall be neutral. The Arbitrator shall have the
authority to assess the costs and expenses of the arbitration proceeding
(including the arbitrators', and attorneys' fees and expenses) against any or
all parties.







<PAGE>

      (f) The Arbitrator shall decide all Disputes and all substantive and
procedural issues related thereto, and shall enforce this Agreement in
accordance with its terms. Without limiting the generality of the previous
sentence, the Arbitrator shall have the authority to issue injunctive relief;
however, the Arbitrator shall not have any power or authority to (i) award
consequential, incidental, indirect or punitive damages or (ii) amend this
Agreement. The Arbitrator shall render the arbitration award, in writing, within
20 days following the completion of the arbitration hearing, and shall set forth
the reasons for the award. In the event that the Arbitrator awards monetary
damages in favor of either party, the Arbitrator must certify in the award that
no indirect, consequential, incidental, indirect or punitive damages are
included in such award. If the Arbitrator's decision results in a monetary
award, the interest to be granted on such award, if any, and the rate of such
interest shall be determined by the Arbitrator in his or her discretion. The
arbitration award shall be final and binding on the parties, and judgment
thereon may be entered in any court of competent jurisdiction, and may not be
appealed except to the extent permitted by the Federal Arbitration Act.

      (4) Continuation of Business. Notwithstanding the existence of any Dispute
or the pendency of any procedures pursuant to this Appendix A, the parties agree
and undertake that all payments not in dispute shall continue to be made and all
obligations not in dispute shall continue to be performed.







<PAGE>

                                   Appendix 1

      (a) First priority shall be given to maximizing the consistency of the
resolution of the Dispute with the satisfaction of all express obligations of
the parties and their Affiliates as set forth in the Agreement.

      (b) Second priority shall be given to resolution of the Dispute in a
manner which best achieves the objectives of the business activities and
arrangements under the Agreement and permits the parties to realize the benefits
intended to be afforded thereby.

      (c) Third priority shall be given to such other matters, if any, as the
parties or the Arbitrator shall determine to be appropriate under the
circumstances.