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                                                                   EXHIBIT 10.5

                               FIFTH AMENDMENT TO
                      UNION TEXAS PETROLEUM HOLDINGS, INC.
                             1985 STOCK OPTION PLAN


         WHEREAS, UNION TEXAS PETROLEUM HOLDINGS, INC. (the "Company") has
heretofore adopted the UNION TEXAS PETROLEUM HOLDINGS, INC. 1985 STOCK OPTION
PLAN (the "Plan"); and

         WHEREAS, subsequent thereto, the Company has amended the Plan; and

         WHEREAS, the Company desires to amend the Plan in certain respects;

         NOW THEREFORE, the Plan shall be amended as follows, effective May 9,
1997:

         1.      Paragraph IV shall be amended by adding (i) the term "Except
as provided below," at the beginning of the first sentence, (ii) "or pursuant
to a qualified domestic relations order as determined by the Committee" at the
end of the first sentence and (iii) the following after the first sentence of
such Section:

         "The Committee may, in its discretion, adopt rules or guidelines under
         which any Option previously granted to an Optionee may be transferred
         (in whole or in part pursuant to such form as approved by the Company)
         by the Optionee to (i) the spouse, children or grandchildren of the
         Optionee ("Immediate Family Members"), (ii) a trust or trusts for the
         exclusive benefit of the Immediate Family Members and, if applicable,
         the Optionee, (iii) a partnership, limited liability company or other
         entity in which such Immediate Family Members and, if applicable, the
         Optionee are the only partners, members or stockholders (iv) the
         transferee pursuant to a qualified domestic relations order as
         determined by the Committee, (v) an organization described under
         Section 501(c)(3) of the Internal Revenue Code of 1986, as amended
         (the "Code") and which is a private foundation within Section 509(a)
         of the Code or any trust the only beneficiary (other than an Immediate
         Family member and, if applicable, the Optionee) of which is an
         organization described under Section 501(c)(3) of the Code and which
         organization is a private foundation within Section 509(a) of the Code
         or (vi) to other persons or entities as approved by the Board or the
         Committee in its discretion.  Following transfer, any such Option
         shall continue to be subject to the same terms and conditions as were
         applicable to the Option immediately prior to transfer; provided,
         however, that no transferred Option shall be exercisable or payable,
         as the case may be, unless arrangements satisfactory to the Company
         have been made to satisfy any tax withholding obligations the Company
         may have with respect to the Option."

         2.      Paragraph VIII shall be amended by adding (i) the term "Except
as provided in Paragraph IV," at the beginning of the first sentence of such
Section and (ii) the following phrase ", which arrangement in the discretion of
the Committee may include the
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relinquishment of a portion of the shares subject to the Option or delivery of
shares of Stock owned by the Optionee" to the end of Paragraph VIII(b), before
the last word "and".

         3.      As amended hereby, the Plan is specifically ratified and
                 reaffirmed.

         IN WITNESS WHEREOF, this Fifth Amendment has been executed this 9th
day of May, 1997.

                                        UNION TEXAS PETROLEUM HOLDINGS, INC.



                                        By: /s/ J. L. WHITMIRE                 
                                           ------------------------------------
                                            J. L. Whitmire
                                            Chairman and Chief Executive Officer

ATTEST:



/s/ LINDA L. MEAGHER                       
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L. L. Meagher
Assistant Secretary