EXHIBIT 4.48



              Supplemental Agreement to the Undertaking Agreement

This Supplemental Agreement is made on 8 December 2005

BETWEEN:

(1)   CHINA NATIONAL OFFSHORE OIL CORPORATION whose legal address is at
      Jingxin Plaza, A2 Dongsanhuanbei Road, Chaoyang District, Beijing
      100027, the People's Republic of China ("CNOOC"); and

(2)   CNOOC LIMITED, whose registered office is at 65th Floor, Bank of China
      Tower, 1 Garden Road, Hong Kong (the "Company").

WHEREAS:

(1)      CNOOC and the Company entered into an undertaking agreement (the
         "Undertaking Agreement") on 6 April 2000 and a supplemental agreement
         to the Undertaking Agreement on 21 December 2000 (the "First
         Supplemental Agreement").

(2)      The parties have agreed to enter into this Supplemental Agreement to
         amend the Undertaking Agreement (as amended by the First Supplemental
         Agreement).

The parties agree as follows in relation to the amendment of the Undertaking
Agreement:

1.    CONDITIONS PRECEDENT

1.1   The provisions of this Supplemental Agreement (other than this clause
      and Clauses 5 and 6) are subject to the approval of the independent
      shareholders of the Company (if required by law or regulation).

1.2   Each of the parties shall use its best endeavours to procure the
      fulfilment of the conditions contained in clause 1.1.

2.    DEFINITION AND INTERPRETATION



                                Exhibit 4.48-1
<PAGE>

      Words and terms used in this Supplemental Agreement shall, save where
      the context otherwise requires, have the same meaning as defined in the
      Undertaking Agreement (as amended by the First Supplemental Agreement).

3.    PRIORITY TO BUSINESS OPPORTUNITIES

      The parties hereby agree that notwithstanding the terms of the
      Undertaking Agreement, the Company may offer to CNOOC any opportunities
      falling within the scope of the Business which are within the onshore
      areas of the PRC or outside the PRC and which the board of directors of
      the Company does not consider is in the best interests of the Company to
      pursue ("Business Opportunity"). If the board of directors of the
      Company decides to offer any such Business Opportunity to CNOOC, CNOOC
      or members of the CNOOC Group will thereafter be entitled to engage in,
      develop and operate such Business Opportunity without restriction,
      subject to Clause 4 below.

4.    OPTION OF ACQUISITION

      For any Business Opportunity afforded to and accepted by CNOOC or
      members of the CNOOC Group in accordance with Clause 3 above, CNOOC
      hereby irrevocably grants to the Company the right to acquire the
      businesses developed by CNOOC or members of the CNOOC Group from such
      Business Opportunity according to the terms of this Clause 4 ("Option of
      Acquisition").

4.1   Option Period: The Company may exercise the option of acquisition at any
      time following an offer made under Clause 3.

4.2   Preliminary Notice of Intention for Acquisition: In order to exercise
      the Option of Acquisition, the Company should issue a preliminary notice
      of intention for acquisition, which shall state that the Company is
      interested in the acquisition of such Business which is being operated
      by CNOOC or members of the CNOOC Group.

4.3   Assets Valuation: After receiving the preliminary notice of intention,
      CNOOC should appoint a qualified valuation institution, which is
      mutually accepted by the parties, in accordance with the laws of the PRC
      to carry out assets valuation on the business that is proposed to be
      acquired, and the basis of valuation shall be determined through
      consultation of the parties. The valuation report should be confirmed by
      the competent PRC government authority or other institutions authorized
      by it. Such valuation report, after confirmation, shall be binding on
      both parties. CNOOC should provide the original of the valuation report
      to the Company within 10 days after the confirmation of the valuation
      report.

4.4   Acquisition Price and Acquisition Agreement: The acquisition price
      should be



                                Exhibit 4.48-2
<PAGE>

      based on the confirmed assets valuation amount, and be determined by the
      parties through negotiation according to the normal commercial terms and
      conditions. The acquisition agreement should be finalized by the parties
      through negotiation according to the normal commercial terms and
      conditions.

4.5   If it is stipulated by law or the relevant listing rules, or considered
      necessary by the majority of the independent directors of the board of
      directors of the Company, that the Company should retain auditors,
      independent financial advisors, valuators outside the PRC, independent
      technology advisors and/or other professional advisors to carry out
      audit and valuation of the business proposed to be acquired and issue
      reports, CNOOC should assist the relevant professional advisors, and
      provide the relevant information to them. All the fees of such advisors
      should be borne by the Company.

4.6   Notice of the Exercise of Option of Acquisition: After receiving the
      confirmed assets valuation report, the board of directors of the Company
      should finish its internal approval procedures in accordance with the
      laws, regulations and listing rules of the PRC and the place of listing
      and the stipulations of the Articles of Association of the Company, and
      notify CNOOC in writing of its decision within 90 days or within such
      period as otherwise agreed between the parties. If the Company decides
      to exercise the Option of Acquisition, it should issue to CNOOC a notice
      of the exercise of Option of Acquisition; if the Company decides not to
      exercise the Option of Acquisition, it should also notify CNOOC in
      writing. If the Company fails to notify CNOOC of its decision in writing
      within 90 days after it receives the confirmed valuation report, or
      within such period as otherwise agreed between the parties, it shall be
      deemed to giving up the Option of Acquisition.

4.7   Exercise of the Option of Acquisition by the Company: The parties shall
      sign the acquisition agreement, and, upon approval of the independent
      shareholders of the Company (if required by law or regulation), the
      Company shall make payment to CNOOC according to the price and method of
      payment provided in the acquisition agreement and shall receive all
      necessary legal rights to the business acquired.



5.     This Supplemental Agreement is supplemental to and forms an integral
       part of the Undertaking Agreement, and shall come into effect as from
       the date of its signing by the duly authorized representatives of both
       parties. Unless otherwise agreed in this Supplemental Agreement, other
       clauses of the Undertaking Agreement are still valid.



                                Exhibit 4.48-3
<PAGE>

CHINA NATIONAL OFFSHORE OIL CORPORATION

Authorized Representative:
Name:
Position:



CNOOC LIMITED

Authorized Representative:
Name:
Position:



                                Exhibit 4.48-4