INCREASED OFFER
                                       BY
                        UNION OIL COMPANY OF CALIFORNIA
                                  TO EXCHANGE

                        0.74 OF A SHARE OF COMMON STOCK

           (INCLUDING THE ASSOCIATED PREFERRED STOCK PURCHASE RIGHTS)

                                       OF

                               UNOCAL CORPORATION
                                      FOR
                     EACH OUTSTANDING SHARE OF COMMON STOCK

                                       OF

                              PURE RESOURCES, INC.


  THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT NEW YORK CITY
        TIME, ON FRIDAY, OCTOBER 25, 2002, UNLESS THE OFFER IS EXTENDED.



                                                                October 11, 2002


To Brokers, Dealers, Commercial Banks,
Trust Companies and Other Nominees:


     Union Oil Company of California, a California corporation (the "Offeror"),
and a subsidiary of Unocal Corporation, a Delaware corporation ("Unocal"), has
amended its offer to exchange each outstanding share of Common Stock, par value
$0.01 per share (collectively, the "Shares"), of Pure Resources, Inc., a
Delaware corporation ("Pure"), by increasing the consideration offered to 0.74
of a share of Common Stock, par value $1.00 per share, of Unocal (together with
the associated preferred share purchase rights, the "Unocal Shares") and cash in
lieu of fractional shares, upon the terms and subject to the conditions set
forth in the Unocal Prospectus, dated October 11, 2002 (the "Prospectus"), and
in the related Letter of Transmittal (which, as amended or supplemented from
time to time, collectively constitute the "Offer"). We have been appointed by
the Offeror to act as Dealer Manager in connection with the Offer.


     Please furnish copies of the enclosed materials to those of your clients
for whose accounts you hold Shares registered in your name or in the name of
your nominee.

     The Offer is conditioned upon a sufficient number of Shares being validly
tendered and not properly withdrawn prior to the expiration of the Offer such
that, giving effect to the Offer, Offeror owns at least 90% of the total number
of outstanding Shares. The Offer is also subject to other terms and conditions
described in the Prospectus.

     Enclosed herewith for your information and forwarding to your clients are
copies of the following documents:


          1.  The Prospectus, dated October 11, 2002.


          2.  The Letter of Transmittal for your use to tender Shares and for
     the information of your clients. Manually signed copies of the Letter of
     Transmittal may be used to tender Shares.

          3.  A printed form of letter which may be sent to your clients for
     whose accounts you hold Shares registered in your name or in the name of
     your nominee, with space provided for obtaining such clients' instructions
     with regard to the Offer.

          4.  Guidelines of the Internal Revenue Service for Certification of
     Taxpayer Identification Number on Substitute Form W-9.

          5.  A return envelope addressed to Mellon Investor Services LLC (the
     "Exchange Agent and Depositary").


     YOUR PROMPT ACTION IS REQUESTED. WE URGE YOU TO CONTACT YOUR CLIENTS AS
PROMPTLY AS POSSIBLE. PLEASE NOTE THAT THE OFFER AND WITHDRAWAL RIGHTS WILL
EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON FRIDAY, OCTOBER 25, 2002,
UNLESS THE OFFER IS EXTENDED.


     In order to accept the Offer, a duly executed and properly completed Letter
of Transmittal and any required signature guarantees, or an "agent's message"
(as defined in the Prospectus) in connection with a book-entry delivery of


Shares, and any other required documents should be sent to the Exchange Agent
and Depositary and either Share Certificates representing the tendered Shares
should be delivered to the Exchange Agent and Depositary, or Shares should be
tendered by book-entry transfer into the Exchange Agent and Depositary's account
maintained at one of the Book Entry Transfer Facilities (as described in the
Prospectus), all in accordance with the instructions set forth in the Letter of
Transmittal and the Prospectus. TENDERS BY NOTICE OF GUARANTEED DELIVERY WILL
NOT BE ACCEPTED.

     The Offeror will not pay any commissions or fees to any broker, dealer or
other person, other than the Dealer Manager, for soliciting tenders of Shares
pursuant to the Offer. The Offeror will, however, upon request, reimburse you
for customary clerical and mailing expenses incurred by you in forwarding any of
the enclosed materials to your clients.

     Any inquiries you may have with respect to the Offer should be addressed
to, and additional copies of the enclosed material may be obtained from, the
Dealer Manager at the address and telephone number set forth on the back cover
of the Prospectus.

                                        Very truly yours,

                                        MERRILL LYNCH & CO.

     NOTHING CONTAINED HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU
OR ANY OTHER PERSON THE AGENT OF UNOCAL, THE OFFEROR, PURE, THE DEALER MANAGER,
OR THE EXCHANGE AGENT AND DEPOSITARY, OR ANY AFFILIATE OF ANY OF THEM, OR
AUTHORIZE YOU OR ANY OTHER PERSON TO MAKE ANY STATEMENT OR USE ANY DOCUMENT ON
BEHALF OF ANY OF THEM IN CONNECTION WITH THE OFFER OTHER THAN THE ENCLOSED
DOCUMENTS AND THE STATEMENTS CONTAINED THEREIN.