<PAGE>
                                                                    EXHIBIT 10.1

                                 AMENDMENT NO. 4

                                     TO THE

                                NOBLE CORPORATION
                     1992 NONQUALIFIED STOCK OPTION PLAN FOR
                             NON-EMPLOYEE DIRECTORS

            WHEREAS, Noble Corporation, a Cayman Islands exempted company
limited by shares (the "Corporation"), has previously assumed the Noble
Corporation 1992 Nonqualified Stock Option Plan for Non-Employee Directors (the
"1992 Plan");

            WHEREAS, pursuant to Section 5.01 of the 1992 Plan, the Board of
Directors has the right under the conditions specified therein to amend the 1992
Plan without obtaining the prior approval of the members of the Corporation; and

            WHEREAS, the Board of Directors of the Corporation has determined
that certain amendments to the 1992 Plan are appropriate and in the best
interests of the Corporation and its members;

            NOW THEREFORE, the Corporation does hereby amend the 1992 Plan,
effective from and after the date hereof, as follows:

      1. Section 1.01 of the 1992 Plan is hereby amended by adding a new
paragraph "(o)" thereto, such paragraph to read in its entirety as follows:

      "(o) "Immediate Family Members" means the spouse, former spouse, children
(including stepchildren) or grandchildren of an individual."

      2. Section 3.02(f) of the 1992 Plan is hereby deleted in its entirety and
the following is substituted therefor:

            "(f) Transferability. No Option shall be transferable, other than by
      will or the laws of descent and distribution, or the rules thereunder, or
      pursuant to a qualified domestic relations order as defined in the Code or
      Title I of the Employee Retirement Income Security Act of 1974, as
      amended, and may be exercised during the life of the Optionee only by the
      Optionee, except as otherwise provided herein below. Notwithstanding the
      foregoing, all or a portion of the Options granted to an Optionee may be
      transferred by such Optionee (i) by gift to the Immediate Family Members
      of such Optionee, partnerships whose only partners are such Optionee or
      the Immediate Family Members of such Optionee, limited liability companies
      whose only shareholders or members are such Optionee or the Immediate
      Family Members of such Optionee, and trusts established solely for the
      benefit of such Optionee or the Immediate Family Members of such Optionee,
      or (ii) to any other persons or entities in the discretion of the Board;
      provided, that subsequent transfers of transferred Options shall be
      prohibited

<PAGE>

      except those in accordance with this Section (by will or the laws of
      descent and distribution). Following transfer, any such Options shall
      continue to be subject to the same terms and conditions as were applicable
      immediately prior to transfer; provided, that for purposes of the Plan and
      any stock option agreement under the Plan, the term "Optionee" shall be
      deemed to refer to the transferee. The events of any termination of
      association set forth in Section 3.02(e) of the Plan and in the stock
      option agreement shall continue to be applied with respect to the original
      Optionee, following which the transferred Options shall be exercisable by
      the transferee only to the extent, and for the periods, specified in
      Section 3.02(e) of the Plan and in the stock option agreement."

      3. This Amendment No. 4 shall amend only those provisions of the 1992 Plan
set forth herein, and those sections, subsections, phrases or words not
expressly amended hereby shall remain in full force and effect.

            IN WITNESS WHEREOF, the undersigned has executed this Amendment as
of the 24th day of April, 2003.


                                        NOBLE CORPORATION


                                        By: /s/ JAMES C. DAY
                                            ----------------------
                                        Name:   James C. Day
                                        Title:  Chairman and Chief
                                                Executive Officer



<PAGE>

  The following is a composite copy of the Noble Corporation 1992 Nonqualified
  Stock Option Plan For Non-Employee Directors as amended through April 24 2003
                               (Amendment No. 4).

                                NOBLE CORPORATION
                       1992 NONQUALIFIED STOCK OPTION PLAN
                           FOR NON-EMPLOYEE DIRECTORS

                                    RECITALS

      A. Effective as of December 17, 1992, the Board of Directors of the
Company (as defined below) hereby adopts this 1992 Nonqualified Stock Option
Plan for Non-Employee Directors.

      B. It is the purpose of the Plan (as defined below) to promote the
interests of the Company and its members by attracting, retaining and
stimulating the performance of qualified directors by giving them the
opportunity to acquire a proprietary interest in the Company and an increased
personal interest in it continued success and progress.

                                    ARTICLE I

                                     GENERAL

      1.01 Definitions. As used herein the following terms shall have the
following meanings:

      (a)   "Board" means the Board of Directors of the Company.

      (b)   "Code" means the Internal Revenue Code of 1986, as amended.

      (c)   "Company" means Noble Corporation, a Cayman Islands exempted company
            limited by shares, and its successors.

      (d)   "Director" means a member of the Board and does not include any
            person named as a director emeritus pursuant to the articles of
            association of the Company.

      (e)   "Effective Date" means December 17, 1992, the date of adoption of
            the Plan by the Board, subject to stockholder approval.

      (f)   "Employee" means any employee of the Company or any parent or
            subsidiary corporation of the Company within the meaning of Sections
            424(e) and (f) of the Code.

      (g)   "Fair Market Value" means (1) the average of the closing sales
            prices of the Ordinary Shares for the 10 business days immediately
            preceding the date in question, as reported of the NASDAQ National
            Market (if the Ordinary Shares



<PAGE>

            are not listed for trading on a national securities exchange) or as
            reported on a national securities exchange (if the Ordinary Shares
            are listed for trading on such exchange), or (2) if the Ordinary
            Shares are not listed for trading on a national securities exchange
            or is not listed as a national market security of NASDAQ or any
            similar system then in use, then the average of the mean between the
            bid and asked prices of the Ordinary Shares for the 10 business days
            immediately preceding the date in question, as reported by the
            National Association of Securities Dealers, Inc.

      (h)   "Grant Date" shall have the meaning assigned to such term in Section
            3.02(a) hereof.

      (i)   "Non-Employee Director" shall mean an individual who (1) is now, or
            hereafter becomes, a Director by virtue of an election (a) by the
            members of the Company, or (b) to the extent permitted under
            applicable law and the articles of association of the Company, by
            the Board for the purpose of filling a vacancy on the Board
            resulting from the death, disability, resignation, removal or
            retirement of a Director or from an increase in the number of
            persons constituting the entire Board, (2) is neither an Employee
            nor an officer of the Company (i.e., an individual elected or
            appointed by the Board or chosen in such other manner as may be
            prescribed in the articles of association of the Company to serve as
            such) and (3) has not elected to decline to participate in the Plan
            with respect to a particular Option pursuant to Section 3.01 hereof.

      (j)   "Option" means any option to purchase Ordinary Shares granted
            pursuant to the Plan.

      (k)   "Optionee" means a Non-Employee Director who has been granted an
            Option.

      (l)   "Option Period" shall have the meaning assigned to such term in
            Section 3.02(d) hereof.

      (m)   "Ordinary Shares" means the Ordinary Shares, par value US$0.10 per
            share, of the Company.

      (n)   "Plan" shall mean this 1992 Nonqualified Stock Option Plan for
            Non-Employee Directors, as it may be amended from time to time.

      (o)   "Immediate Family Members" means the spouse, former spouse, children
            (including stepchildren) or grandchildren of an individual.

      1.02 Options. The Options shall be options that are not qualified as
"incentive stock options" under Section 422 of the Code.



<PAGE>

                                   ARTICLE II

                                 ADMINISTRATION

      The Plan shall be administered by the Board. The Board shall have no
authority, discretion or power to select the Non-Employee Directors who will
receive Options or to set the number of shares to be covered by each Option. The
Board shall have no authority, discretion or power to set the exercise price or
the period within which Options may be exercised, or to alter any other terms or
conditions specified herein, except in the sense of administering the Plan
subject to the express provisions hereof, including Section 5.01.

      Subject to the foregoing limitations, the Board shall have authority and
power to adopt such rules and regulations and to take such action as it shall
consider necessary or advisable for the administration of the Plan, and to
construe, interpret and administer the Plan. The decisions of the Board relating
to the Plan shall be final and binding upon the Company, the Non-Employee
Directors, the Optionees and all other persons. No member of the Board shall
incur any liability by reason of any action or determination made in good faith
with respect to the Plan or any stock option agreement entered into pursuant to
the Plan.

                                   ARTICLE III

                                GRANT OF OPTIONS

      3.01 Participation. Each Non-Employee Director shall be granted Options on
the terms and conditions herein described. A Director otherwise eligible to
participate in the Plan may elect to decline to accept any Option by giving
notice thereof to the Company or by refusing to execute a stock option agreement
relating to such Option.

      3.02 Stock Option Agreements. Each Option shall be evidenced by a written
stock option agreement, which agreement shall be entered into by the Company and
the Non-Employee Director to whom the Option is granted. Each such agreement
shall include, incorporate or conform to the following terms and conditions, and
such other terms and conditions not inconsistent therewith or with the terms and
conditions of this Plan as the Board considers appropriate in each case:

            (a) Option Grant Date. On the next business day after each annual
general meeting of members of the Company occurring after the Effective Date,
Options shall be granted automatically to each person who is a Non-Employee
Director on such date. The date of grant of an Option as set forth herein shall
be referred to hereinafter as the "Grant Date" of such Option.

            (b) Number. Each Non-Employee Director shall automatically be
granted an Option to purchase 10,000 Ordinary Shares on the first Grant Date
occurring after such person begins serving. Thereafter, each Non-Employee
Director serving on a Grant Date shall automatically be granted, as of such
date, an Option to purchase 7,500 Ordinary Shares. If on the Grant Date of any
Option fewer Ordinary Shares remain available for grant under the Plan than are
necessary to permit the grant of Options in accordance with the provisions of
this



<PAGE>

Section 3.02, then (i) first, an Option covering an equal number of whole
Ordinary Shares, up to 10,000 shares, shall be granted on such date to each
Non-Employee Director who has not previously been granted an Option and (ii)
thereafter, Options shall be granted to the remaining Non-Employee Directors
then serving covering an equal number of whole Ordinary Shares and all such
Options shall cover, in the aggregate, all remaining Ordinary Shares then
available for grant under the Plan.

            (c) Price. The exercise price under each Option shall be the Fair
Market Value per Ordinary Share on the Grant Date.

            (d) Option Period. Each Option shall be exercisable from time to
time over a period (i) commencing upon the earlier of (A) the date that is one
year following the Grant Date of such Option and (B) the day immediately prior
to the date of the next annual general meeting of members occurring following
such Grant Date, provided that the date of such annual general meeting of
members is at least 355 days after such Grant Date, and (ii) ending upon the
expiration of ten years from the Grant Date (the "Option Period"), unless
terminated sooner pursuant to the provisions described in Section 3.02(e) below.

            (e) Termination of Services, Death, Etc. Each stock option agreement
shall provide as follows with respect to the exercise of the Option evidenced
thereby in the event that the Optionee ceases to be a Director for the reasons
described in this Section 3.02(e):

                  (i) If the Optionee ceases to be a Director on account of such
            Optionee's (a) fraud or intentional misrepresentation, or (b)
            embezzlement, misappropriation or conversion of assets or
            opportunities of the Company or any direct or indirect
            majority-owned subsidiary of the Company, then the Option shall
            automatically terminate and be of no further force or effect as of
            the date the Optionee ceases to be a Director;

                  (ii) If the Optionee shall die during the Option Period while
            a Director (or during the additional five-year period provided by
            paragraph (iii) of this Section 3.02(e)), the Option may be
            exercised, to the extent that the Optionee was entitled to exercise
            it at the date of the Optionee's death, within five years after such
            death (if otherwise within the Option Period), but not thereafter,
            by the executor or administrator of the estate of such Optionee, or
            by the person or persons who shall have acquired the Option directly
            from the Optionee by bequest or inheritance; or

                  (iii) If an Optionee ceases to be a Director for any reason
            (other than the circumstances specified in paragraphs (i) and (ii)
            of this Section 3.02(e)) within the Option Period, the Option may be
            exercised, to the extent the Optionee was able to do so at the date
            of termination of the directorship, within five years after such
            termination (if otherwise within the Option Period), but not
            thereafter.

            (f) Transferability. No Option shall be transferable, other than by
will or the laws of descent and distribution, or the rules thereunder, or
pursuant to a qualified domestic



<PAGE>

relations order as defined in the Code or Title I of the Employee Retirement
Income Security Act of 1974, as amended, and may be exercised during the life of
the Optionee only by the Optionee, except as otherwise provided herein below.
Notwithstanding the foregoing, all or a portion of the Options granted to an
Optionee may be transferred by such Optionee (i) by gift to the Immediate Family
Members of such Optionee, partnerships whose only partners are such Optionee or
the Immediate Family Members of such Optionee, limited liability companies whose
only shareholders or members are such Optionee or the Immediate Family Members
of such Optionee, and trusts established solely for the benefit of such Optionee
or the Immediate Family Members of such Optionee, or (ii) to any other persons
or entities in the discretion of the Board; provided, that subsequent transfers
of transferred Options shall be prohibited except those in accordance with this
Section (by will or the laws of descent and distribution). Following transfer,
any such Options shall continue to be subject to the same terms and conditions
as were applicable immediately prior to transfer; provided, that for purposes of
the Plan and any stock option agreement under the Plan, the term "Optionee"
shall be deemed to refer to the transferee. The events of any termination of
association set forth in Section 3.02(e) of the Plan and in the stock option
agreement shall continue to be applied with respect to the original Optionee,
following which the transferred Options shall be exercisable by the transferee
only to the extent, and for the periods, specified in Section 3.02(e) of the
Plan and in the stock option agreement.

            (g) Agreement to Continue in Service. Each Optionee shall agree to
remain in the service of the Company, at the pleasure of the Company's members,
for a continuous period extending at least through the earlier of (i) the date
that is one year following the Grant Date of the Option and (ii) the day
immediately prior to the date of the next annual meeting of members occurring
following such Grant Date, at the retainer rate and fee schedule then in effect
or at such changed rate or schedule as the Company from time to time may
establish; provided, that nothing in the Plan or in any stock option agreement
evidencing an Option shall confer upon such Optionee any right to continue as a
Director.

            (h) Exercise, Payments, Etc. Each stock option agreement between the
Company and an Optionee shall provide that the method for exercising the Option
evidenced thereby shall be by delivery to the President of the Company by United
States registered or certified mail, postage prepaid, addressed to the Company,
or by hand delivery, of written notice signed by the Optionee specifying the
number Ordinary Shares with respect to which such Option is being exercised.
Upon exercise of an Option, the purchase price for the Ordinary Shares purchased
shall be paid in full by cash or check; provided, however, that at the request
of an Optionee and to the extent permitted by applicable law, the Company shall
approve reasonable arrangements with such Optionee and a brokerage firm under
which such Optionee may exercise an Option by properly delivering notice of
exercise, together with such other documents as the Company shall require, and
the Company shall, upon payment in full by cash or check of the purchase price
and any other amounts due in respect of such exercise, deliver to such
Optionee's brokerage firm one or more certificates representing Ordinary Shares
issued in respect of such exercise.

            Any notice given hereunder shall be deemed to be given on the date
on which the same was deposited in a regularly maintained receptacle for the
deposit of United States mail, addressed and sent as above-stated, or, in the
case of hand delivery, on the date of delivery to the



<PAGE>

President of the Company. The proceeds of any sale of Ordinary Shares covered by
Options shall constitute general funds of the Company. Upon exercise of an
Option, the Optionee will be required to pay to the Company the amount of any
federal, state or local taxes required by law to be withheld in connection with
such exercise.

                                   ARTICLE IV

                           AUTHORIZED ORDINARY SHARES

      4.01 Ordinary Shares. The total number of Ordinary Shares as to which
Options may be granted shall be 650,000, in the aggregate, except as such number
of shares shall be adjusted from and after the Effective Date in accordance with
the provisions of Section 4.02 hereof. If any outstanding Option shall expire or
be terminated for any reason before the end of the Option Period, the Ordinary
Shares allocable to the unexercised portion of such Option shall again be
subject to the Plan. The Company shall, at all times during the life of any
outstanding Options, retain as authorized and unissued Ordinary Shares at least
the number of shares from time to time included in the outstanding Options or
otherwise assure itself of its ability to perform its obligations under the
Plan.

      4.02 Adjustments Upon Changes in Ordinary Shares. In the event the Company
shall effect a split of the Ordinary Shares or dividend payable in Ordinary
Shares, or in the event the outstanding Ordinary Shares shall be combined into a
smaller number of shares, the maximum number of shares as to which Options may
be granted shall be increased or decreased proportionately. In the event that
before delivery by the Company of all of the Ordinary Shares in respect of which
any Option has been granted, the Company shall have effected such a split,
dividend or combination, the shares still subject to the Option shall be
increased or decreased proportionately and the purchase price per share shall be
increased or decreased proportionately so that the aggregate purchase price for
all the then optioned shares shall remain the same as immediately prior to such
split, dividend or combination.

      In the event of a reclassification of the Ordinary Shares not covered by
the foregoing, or in the event of a liquidation, separation or reorganization,
including a merger, consolidation or sale of assets, the Board shall make such
adjustments, if any, as it may deem appropriate in the number, purchase price
and kind of shares covered by the unexercised portions of Options theretofore
granted. The provisions of this Section 4.02 shall only be applicable if, and
only to the extent that, the application thereof does not conflict with any
valid governmental statute, regulation or rule.

                                    ARTICLE V

                               GENERAL PROVISIONS

      5.01 Amendment, Suspension or Termination of Plan. Subject to the
limitations set forth in this Section 5.01, the Board may from time to time
amend, modify, suspend or terminate the Plan. Nevertheless, no such amendment,
modification, suspension or termination shall (a) impair any Options theretofore
granted or (b) be made without the approval of the members of



<PAGE>

the Company where such change would (i) materially increase the total number of
Ordinary Shares which may be issued under the Plan (other than as provided in
Section 4.02 hereof), (ii) materially modify the requirements as to eligibility
for participation in the Plan, (iii) materially increase the benefits accruing
to participants under the Plan or (iv) have the effect of providing for the
grant of options to purchase Ordinary Shares at less than the fair market value
per share thereof on the applicable Grant Date. Notwithstanding any other
provision of this Section 5.01, the provisions of the Plan governing (A) the
number of Ordinary Shares covered by each Option, (B) the exercise price per
Ordinary Share under each Option, (C) when and under what circumstances each
Option will be granted and (D) the period within which each Option may be
exercised, shall not be amended more than once every six months, other than to
comport with changes in the Code or the rules promulgated thereunder, and the
Employee Retirement Income Security Act of 1974, as amended, or the rules
promulgated thereunder.

      5.02 Effectiveness. This Plan shall become effective as of the Effective
Date, subject to and upon the receipt of stockholder approval by the affirmative
votes of the holders of a majority of the shares of Common Stock present, or
represented, and entitled to vote at a meeting of stockholders duly held in
accordance with the applicable laws of the State of Delaware.

      5.03 Paragraph Headings. The paragraph headings included herein are only
for convenience, and they shall have no effect on the interpretation of the
Plan.

      5.04 Gender. Words of any gender used in the Plan shall be construed to
include any other gender.