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                                                                     EXHIBIT 4.4

                          CERTIFICATE OF INCORPORATION

                                       OF

                        NOBLE HOLDING (U.S.) CORPORATION

                                    ARTICLE I

         The name of the corporation is Noble Holding (U.S.) Corporation (the
"Corporation").

                                   ARTICLE II

         The address of the initial registered office of the Corporation in the
State of Delaware is c/o The Corporation Trust Company, 1209 Orange Street,
Wilmington, County of New Castle, Delaware 19801. The name of the initial
registered agent of the Corporation at such address is The Corporation Trust
Company.

                                   ARTICLE III

         The purpose for which the Corporation is organized is to engage in any
lawful act or activity for which corporations may be organized under the General
Corporation Law of the State of Delaware ("DGCL").

                                   ARTICLE IV

         The Corporation is to have perpetual existence.

                                    ARTICLE V

         The total number of shares of all classes of stock which the
Corporation shall have authority to issue is 10,000 shares of common stock, par
value of $.01 per share ("Common Stock").

                                   ARTICLE VI

         The number of directors constituting the initial Board of Directors is
three (3). Subject to the provisions of law, the number of the directors of the
Corporation may be increased or decreased from time to time pursuant to the
Bylaws of the Corporation (the "Bylaws"). Each director shall serve until the
annual meeting of stockholders next following his election or until his earlier
death, resignation or removal. The act of a majority of the directors present at
a meeting at which a quorum is present shall be the act of the Board of
Directors.

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                                   ARTICLE VII

         The names and addresses of the persons who are to serve as the initial
directors of the Corporation until their respective successors are duly elected
and qualified, or until the term of office shall have otherwise terminated, are
as follows:

<TABLE>
<CAPTION>
     Name                                   Mailing Address
     ----                                   ---------------
<S>                                <C>
Robert D. Campbell                 13135 South Dairy Ashford, Suite 800
                                   Sugar Land, Texas 77478

Mark A. Jackson                    13135 South Dairy Ashford, Suite 800
                                   Sugar Land, Texas 77478

Julie J. Robertson                 13135 South Dairy Ashford, Suite 800
                                            Sugar Land, Texas 77478

</TABLE>

                                  ARTICLE VIII

         The Board of Directors is expressly authorized and empowered to make,
alter or repeal the Bylaws, subject to the power of the stockholders to alter or
repeal the Bylaws.

                                   ARTICLE IX

         The election of directors need not be by written ballot unless the
Bylaws so provide.

                                    ARTICLE X

         To the fullest extent permitted by the DGCL as the same exists or may
hereafter be amended, a director of the Corporation shall not be personally
liable to the Corporation or its stockholders for monetary damages for breach of
duty as a director. Without limiting the foregoing in any respect, a director of
the Corporation shall not be personally liable to the Corporation or its
stockholders for monetary damages for breach of duty as a director, except for
liability (i) for any breach of the director's duty of loyalty to the
Corporation or its stockholders, (ii) for acts or omissions not in good faith or
which involve intentional misconduct or a knowing violation of law, (iii) under
Section 174 of the DGCL, or (iv) for any transaction from which the director
derived an improper personal benefit. If the DGCL is amended to authorize
corporate action further eliminating or limiting the personal liability of
directors, then the liability of a director of the Corporation shall be
eliminated or limited to the fullest extent permitted by the DGCL, as so
amended.

                                   ARTICLE XI

         Any contract or other transaction between the Corporation and one or
more of its directors, between the Corporation and any firm of which one or more
of its directors is a member or of which a director is an employee or in which a
director is otherwise interested, or between the Corporation and any corporation
or association of which one or more of its directors

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are stockholders, members, directors, officers or employees or in which they are
interested shall be valid for all purposes. The foregoing shall be true
notwithstanding the presence of such director or directors at the meeting of the
Board of Directors that acts upon or in reference to such contract or
transaction and notwithstanding his or their participation in such action, if
the fact of such interest shall be disclosed or known to the Board of Directors
and the Board of Directors shall nevertheless authorize, approve and ratify such
contract or transaction by vote of a majority.

                                   ARTICLE XII

         The Corporation reserves the right to alter, amend or repeal any
provision contained in this Certificate of Incorporation in the manner now or
hereafter prescribed by the laws of the State of Delaware. All rights herein
conferred are granted subject to this reservation.

                                  ARTICLE XIII

         The powers of the sole incorporator shall terminate upon filing of this
Certificate of Incorporation. The name and address of the sole incorporator are
as follows:

         Name                               Mailing Address
         ----                               ---------------
         Courtney York                      Baker Botts L.L.P.
                                            2001 Ross Avenue, Suite 800
                                            Dallas, Texas 75201

         THE UNDERSIGNED, being the sole incorporator herein named, for the
purpose of forming a corporation pursuant to the DGCL, does make this
Certificate, hereby declaring and certifying that this is her act and deed and
that the facts herein stated are true, and accordingly has hereunto set her hand
as of the 8th day of March 2002.

                                            /s/ Courtney York
                                            -----------------------------------
                                            Courtney York

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