<PAGE>
                               FIRST AMENDMENT TO
                              AMENDED AND RESTATED
                          LIMITED PARTNERSHIP AGREEMENT

                                       OF

                             EQUISTAR CHEMICALS, LP







<PAGE>

                     FIRST AMENDMENT TO AMENDED AND RESTATED
                          LIMITED PARTNERSHIP AGREEMENT
                                       OF
                             EQUISTAR CHEMICALS, LP

      This First Amendment to the Amended and Restated Limited Partnership
Agreement of Equistar Chemicals, LP, dated as of June, 30, 1998 (the "First
Amendment") is entered into by and among Lyondell Petrochemical G.P. Inc., a
Delaware corporation ("Lyondell GP"), Lyondell Petrochemical L.P. Inc., a
Delaware corporation ("Lyondell LP"), Millennium Petrochemicals GP LLC, a
Delaware limited liability company ("Millennium GP"), Millennium Petrochemicals
LP LLC, a Delaware limited liability company ("Millennium LP"), PDG Chemical
Inc., a Delaware corporation ("Occidental GP"), Occidental Petrochem Partner 1,
Inc., a Delaware corporation ("Occidental LP1"), Occidental Petrochem Partner 2,
Inc., a Delaware corporation ("Occidental LP2"), and Occidental Petrochem
Partner GP, Inc., a Delaware corporation ("New Oxy GP").

      WHEREAS, reference is here made for all purposes to the Amended and
Restated Limited Partnership Agreement of Equistar Chemicals, LP, dated May 15,
1998 (the "Partnership Agreement"); and

      WHEREAS, all capitalized terms that are defined in the Partnership
Agreement, but are not defined in this First Amendment, shall have the same
meanings as defined in the Partnership Agreement; and

      WHEREAS, Occidental GP wishes to convert 294 of its General Partner Units
in the Partnership to Limited Partner Units, and to transfer such Units to
Occidental LP2, and each of the other Partners are willing to consent to such
conversion and transfer; and

      WHEREAS, Occidental GP wishes to transfer its remaining General Partner
Unit to New Oxy GP, and to withdraw from the Partnership, and New Oxy GP wishes
to be admitted to the Partnership as a General Partner, and each of the other
Partners are willing to consent to such transfer, withdrawal, and admission;

      NOW THEREFORE, in consideration of the premises and the mutual covenants
herein contained, the parties hereto agree as follows:

      1. Transfers and Withdrawal. (a) Occidental GP hereby converts 294 of its
295 General Partner Units in the Partnership into 294 Limited Partner Units in
the Partnership.

            (b) Occidental GP does hereby transfer its 294 Limited Partner Units
      to Occidental LP2.

            (c) Occidental GP does hereby transfer its remaining 1 General
      Partner Unit to New Oxy GP. Concurrently, New Oxy GP is hereby admitted
      into the Partnership as a







<PAGE>

      General Partner of the Partnership. Concurrently, Occidental GP hereby
      withdraws from the Partnership.

            (d) New Oxy GP assumes all of the obligations of Occidental GP under
      or in respect of the Partnership.

      2. Amendments. (a) Any reference in the Partnership Agreement to
Occidental GP shall hereafter be deemed for all purposes to mean New Oxy GP.

            (b) As a result of the conversions, the withdrawal and the transfers
      described herein, Section 2.1 of the Partnership Agreement is restated in
      its entirety as follows:

            "2.1 Holdings of Partners. Effective as of the close of business on
      June 30, 1998, the Units shall be owned as follows:

                           Partner         Units
                           -------         -----

                         Lyondell GP        802

                        Millennium GP       590

                        Occidental GP        1

                         Lyondell LP      40,180

                        Millennium LP     28,910

                       Occidental LP1      6,623

                       Occidental LP2     22,876

                            TOTAL        100,000
                            =====        =======

      The Units shall entitle the holder to the distributions set forth in
      Section 3 and to the allocation of Profits, Losses and other items as set
      forth in Section 4. Units shall not be represented by certificates."

      3. References to and Effect on Partnership Agreement. (a) The provisions
of the Partnership Agreement (as amended by this First Amendment) shall remain
in full force and effect in accordance with their terms following the
effectiveness of this First Amendment. Each Partner, by executing this First
Amendment, (i) consents to the admission of New Oxy GP into the Partnership and
as a General Partner, (ii) consents to the withdrawal of PDG Chemical, Inc. as a
General Partner and (iii) ratifies all actions done in contemplation of items
(i) and (ii) herein.

            (b) On and after the date first written above, each reference in the
      Partnership Agreement to "this Agreement", "hereunder", "hereof", "herein"
      or words of like import, and


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<PAGE>

      any reference to the Partnership Agreement in any certificate or document
      delivered in connection therewith, shall mean and be a reference to the
      Partnership Agreement as amended hereby.

            (c) The General Partners shall, or shall cause the Partnership to,
      execute, swear to, acknowledge, deliver, file or record in public offices
      and publish all such certificates, notices, statements or other
      instruments, and take all such other actions, as may be required by law
      for the purpose of reflecting the withdrawals and admissions herein,
      including, but not limited to, an amendment of the Certificate of Limited
      Partnership of the Partnership pursuant to Section 17-204 of the Act.

      4. Representations and Warranties. Each of Occidental GP and New Oxy GP
represent and warrant to the other Partners as follows:

            (a) Due Organization; Good Standing and Power. New Oxy GP is a
      corporation duly organized, validly existing and in good standing under
      the laws of its state of organization. New Oxy GP has all requisite power
      and authority to enter into this First Amendment and to perform its
      obligations hereunder. New Oxy GP is duly authorized, qualified or
      licensed to do business as a foreign corporation and is in good standing
      in the State of Texas and in each of the other jurisdictions in which its
      right, title or interest in or to any of its assets or properties requires
      such authorization, qualification or licensing, except where the failure
      to so qualify or to be in good standing would not reasonably be expected
      to have a material adverse effect.

            (b) Authorization and Validity of Agreements. The execution,
      delivery and performance of this First Amendment by New Oxy GP and the
      consummation by it of the transactions contemplated hereby have been duly
      authorized by the Board of Directors of New Oxy GP. Except to the extent
      heretofore obtained, no other corporate action or action by stockholders
      is necessary for the authorization, execution, delivery and performance by
      New Oxy GP of this First Amendment and the consummation by New Oxy GP of
      the transactions contemplated hereby. This First Amendment has been duly
      executed and delivered by New Oxy GP and constitutes a legal, valid and
      binding obligation of New Oxy GP, enforceable in accordance with its
      terms, except as the same may be limited by bankruptcy, insolvency,
      reorganization, moratorium and other laws relating to or affecting
      creditors' rights generally and by general equity principles.

            (c) No Consents Required; No Conflict with Instruments to which New
      Oxy GP is a Party. The execution, delivery and performance of this First
      Amendment by New Oxy GP, the performance by New Oxy GP of its obligations
      under the Partnership Agreement (as amended by this First Amendment) and
      the consummation by New Oxy GP of the transactions contemplated hereby or
      thereby (i) will not require any consent except for such consents the
      failure of which to be obtained or made, would not in the aggregate
      reasonably be expected to have a material adverse effect; and (ii) will
      not violate (with or without the


                                      -3-






<PAGE>

      giving of notice or the lapse of time or both) or conflict with, or result
      in the breach or termination of any provision of, or constitute a default
      under, or result in the acceleration of the performance of the obligations
      of New Oxy GP, any agreement or instrument to which New Oxy GP is a party,
      except for such obligations, conflicts, breaches, terminations, defaults
      or accelerations or which would not in the aggregate reasonably be
      expected to have a material adverse effect.

      5. Secretary's Certificate. New Oxy GP shall provide to each of the other
General Partners and the Partnership a copy of a secretary's certificate in the
form attached as Appendix I hereto.

      6. Counterparts. This First Amendment may be executed by one or more of
the parties hereto in any number of separate counterparts, and all of such
counterparts taken together shall be deemed to constitute one and the same
instrument.

      7. Governing Law. This First Amendment shall be governed by and construed
in accordance with the laws of the State of Delaware, without giving effect to
any conflicts of law principles.

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<PAGE>

      IN WITNESS WHEREOF, this First Amendment has been executed on behalf of
each of the parties hereto, by their respective officers thereunto duly
authorized, effective as of the date first written above.

                                    GENERAL PARTNERS:

                                    LYONDELL PETROCHEMICAL G.P. INC.

                                    By: /s/ Kerry A. Galvin
                                       ---------------------------------------
                                    Name:
                                    Title:


                                    MILLENNIUM PETROCHEMICALS GP LLC

                                    By:   Millennium Petrochemicals Inc., its
                                          Manager

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


                                   OCCIDENTAL PETROCHEM PARTNER GP, INC.

                                   By: /s/ David C. Yen
                                      ---------------------------------------
                                   Name:  David C. Yen
                                   Title: Vice President and Treasurer


                                   WITHDRAWING GENERAL PARTNER:

                                   PDG CHEMICAL INC.

                                   By: /s/ J.R. Havert
                                      ---------------------------------------
                                   Name:  J.R. Havert
                                   Title: Vice President and Assistant Treasurer


                                       -5-





<PAGE>

                                    LIMITED PARTNERS:

                                    LYONDELL PETROCHEMICAL L.P. INC.

                                    By: /s/ Kerry A. Galvin
                                       --------------------------------------
                                    Name:
                                    Title:


                                    MILLENNIUM PETROCHEMICALS GP LLC

                                    By:   Millennium Petrochemicals Inc., its
                                          Manager

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


                                     OCCIDENTAL PETROCHEM PARTNER GP, INC.

                                     By: /s/ David C. Yen
                                        ---------------------------------------
                                     Name:  David C. Yen
                                     Title: Vice President and Treasurer


                                     WITHDRAWING GENERAL PARTNER:

                                   PDG CHEMICAL INC.

                                   By: /s/ J.R. Havert
                                   ---------------------------------------
                                   Name:  J.R. Havert
                                   Title: Vice President and Assistant Treasurer


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