OCCIDENTAL PETROLEUM CORPORATION

                                                                 October 7, 2003


Credit Suisse First Boston LLC
Eleven Madison Avenue
New York, New York 10010-3629

Ladies and Gentlemen:


     This letter agreement (the "AGREEMENT") is being executed in order to
document our understanding regarding the purchase by us or one of our affiliates
from you in a public offering (the "PUBLIC OFFERING") of registered shares of
common stock, par value $1.00 per share (the "ORIGINAL COMMON STOCK"), of
Lyondell Chemical Company, a Delaware corporation (the "COMPANY").

     The Company proposes to issue and sell to you, and you propose to offer, an
aggregate of 12,000,000 shares (the "UNDERWRITTEN SHARES") and, at your
election, up to 1,800,000 additional shares (the "OPTION SHARES" and together
with the Underwritten Shares, the "SHARES") of Original Common Stock, pursuant
to an underwriting agreement, between the Company and you entered into
concurrently with this Agreement (the "UNDERWRITING Agreement"). As of the date
of this Agreement, excluding 5,000,000 shares of Original Common Stock issuable
upon exercise of a warrant, we beneficially own 36,310,792 shares of the
Company's Series B common stock (the "SERIES B COMMON STOCK", and together with
the Original Common Stock, the "COMMON STOCK"), which represents approximately
22% of the Company's common equity. Unless otherwise provided herein,
capitalized terms used and not defined herein shall have the meanings ascribed
to them in the Underwriting Agreement.

     Subject to the terms and conditions of this Agreement and the closing of
the sale of the Underwritten Shares on the Closing Date, we agree to purchase
from you, in the Public Offering, 2,700,000 shares of Original Common Stock (the
"OXY SHARES") on the Closing Date at the Purchase Price per share specified in
the Underwriting Agreement. Notwithstanding the foregoing, you shall have no
obligation to sell to us any Oxy Shares in the event the Underwriting Agreement
is terminated (for any reason) or in the event the Company fails to deliver such
shares to you, it being understood that the Company shall not be deemed to have
delivered any Oxy Shares on the Closing Date until the Company shall have first
delivered 9,300,000 Underwritten Shares on the Closing Date.

     This Agreement is made in reliance upon our representations and warranties
to you contained in this Agreement. We hereby represent and warrant to you that
the Oxy Shares to be acquired by us will be acquired for investment for our own
account, not as a nominee or agent, and not with a view to the resale or
distribution of any part thereof, and that in connection with the Public
Offering, we will comply with the provisions of Regulation M under the
Securities Exchange Act of 1934, as amended. By executing this Agreement, we
further represent and warrant to you that we do not presently have any contract,
undertaking, agreement or arrangement with any person to sell, transfer or grant
participations to such person or to any third person with respect to, any of the
Oxy Shares.

     We hereby agree on behalf of ourselves and our direct and indirect
subsidiaries (collectively, the "RESTRICTED PARTIES"), that from the date hereof
and until 90 days after the public offering date set forth in the final
prospectus used to sell the Shares (the "PUBLIC OFFERING DATE") pursuant to the
Underwriting Agreement, the Restricted Parties will not offer, sell, contract to
sell, pledge or otherwise dispose of, directly or indirectly, any shares of
Common Stock or securities convertible into or exchangeable or exercisable for
any shares of Common Stock, enter into a transaction which would have the same
effect, or enter into any swap, hedge or other arrangement that disposes of, in
whole or in part, any of the economic consequences of ownership of shares of
Common Stock, whether any such aforementioned transaction is to be settled by
delivery of shares of Common Stock or such other securities, in cash or
otherwise, or publicly disclose the intention to make any such offer, sale,
pledge or disposition, or to enter into any such transaction, swap, hedge or
other arrangement, without, in each case, your prior written consent; provided,
however, that the foregoing restrictions shall not prevent Occidental from
making public statements concerning its long term expectations for its
investment in the Company so long as Occidental does not state any specific plan
or proposal to sell. In addition, we agree that, without your prior written
consent, the Restricted Parties will not, during the period commencing on the



date hereof and ending 90 days after the Public Offering Date, make any demand
for or exercise any right with respect to, the registration of any shares of
Common Stock or any security convertible into or exercisable or exchangeable for
shares of Common Stock. Any shares of Common Stock received upon exercise of
warrants or the payment of in-kind dividends will also be subject to the
foregoing restrictions of this paragraph. The foregoing restrictions of this
paragraph shall not apply to our purchase of shares of Original Common Stock in
open market transactions after the Closing Date pursuant to Section 2.2(b) of
the Stockholders Agreement among the Company and the Stockholders named therein,
dated August 22, 2002.

     In furtherance of the foregoing, the Company and its transfer agent and
registrar are hereby authorized to decline to make any transfer of shares of
Common Stock if such transfer would constitute a violation or breach of this
Agreement.

     If the Underwriting Agreement is terminated for any reason, this Agreement
(including, without limitation, our obligations in the second immediately
preceding paragraph) shall also terminate at the time of such termination. You
shall have no liability to the undersigned arising out of any termination of the
Underwriting Agreement or the failure to consummate the transaction contemplated
therein and the undersigned acknowledges that you have the right to terminate
the Underwriting Agreement and/or to decline to consummate the transaction
contemplated therein under certain circumstances. This Agreement shall be
binding on us and our successors and assigns.

     THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE
LAWS OF THE STATE OF NEW YORK (WITHOUT REFERENCE TO THE CHOICE OF LAW RULES
THEREOF).



                                        Very truly yours,


                                        OCCIDENTAL PETROLEUM CORPORATION


                                        /s/ STEPHEN I. CHAZEN
                                        --------------------------------

                                        Name:  Stephen I. Chazen
                                        Title: Chief Financial Officer and
                                               Executive Vice President -
                                               Corporate Development



Accepted as of the date hereof:

CREDIT SUISSE FIRST BOSTON LLC



/s/ DAVID P. FARIS
------------------------------
Name:  David P. Faris
Title: Director