Exhibit 2(b)

                            STOCK OPTION AGREEMENT


     STOCK OPTION AGREEMENT (the "Agreement"), dated as of June 9, 1997, by and
between NUMAR Corporation, a Pennsylvania corporation (the "Company"), and
Halliburton Company, a Delaware corporation (the "Grantee").

                                   RECITALS

     The Grantee, the Company and Halliburton M.S. Corp., a Delaware corporation
and a wholly owned subsidiary of the Grantee ("Newco") propose to enter into an
Agreement and Plan of Merger dated as of the date hereof (the "Plan") providing,
among other things, for the merger (the "Merger") of Newco with and into the
Company which shall be the surviving corporation.

     The Board of Directors of the Company has recommended the approval of the
Plan by the stockholders of the Company.

     As a condition and inducement to the Grantee's willingness to enter into
the Plan, the Grantee has requested that the Company agree, and the Company has
agreed, to grant the Grantee the Option (as defined below).

     NOW, THEREFORE, in consideration of the foregoing and the respective
representations, warranties, covenants and agreements set forth herein and in
the Plan, the Company and the Grantee agree as follows:

     1.   Capitalized Terms.  Capitalized terms used but not defined herein are
defined in the Plan and are used herein with the same meanings as ascribed to
them therein; provided, however, that, as used in this Agreement, "Person" shall
have the meaning specified in Sections 3(a)(9) and 13(d)(3) of the Exchange Act.

     2.   Grant of Option.  Subject to the terms and conditions set forth
herein, the Company hereby grants to the Grantee an irrevocable option (the
"Option") to purchase, out of the authorized but unissued Company Common Stock,
a number of shares equal to up to 15.0% of the shares of Company Common Stock
outstanding as of the date hereof (as adjusted as set forth herein) (the "Option
Shares"), at a purchase price of $36.00 per Option Share (the "Exercise Price").

     3.   Term.  The Option shall be exercisable and shall remain in full force
and effect until the earliest to occur of (i) the Effective Time, (ii) the first
anniversary of the receipt by Grantee of written notice from the Company of the
occurrence of an Exercise Event (as hereinafter defined) or (iii) termination of
the Plan prior to the occurrence of an Exercise Event (the "Option Term").  The

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rights and obligations set forth in Sections 7, 8, 9 and 10 shall not terminate
at the expiration of the Option Term, but shall extend to such time as is
provided in those Sections.

     4.   Exercise of Option.

          (a) The Grantee may exercise the Option, in whole or in part, at any
     time and from time to time during the Option Term following the occurrence
     of an Exercise Event. Notwithstanding the expiration of the Option Term,
     the Grantee shall be entitled to purchase those Option Shares with respect
     to which it has exercised the Option in accordance with the terms hereof
     prior to the expiration of the Option Term.

          (b) As used herein, an "Exercise Event" shall mean any of the
     following events:
 
               (i) any Person (other than the Grantee or any Affiliate of the
          Grantee) shall have commenced (as such term is defined in Rule 14d-2
          under the Exchange Act) a tender or exchange offer to purchase any
          shares of Company Common Stock such that, upon consummation of such
          offer, such Person would own or control 35% or more of the then
          outstanding Company Common Stock and the Board of Directors of the
          Company, within ten Business Days thereafter, either fails to
          recommend against acceptance of such tender or exchange offer by the
          Company's shareholders or takes no position with respect thereto; or

               (ii) any Person (other than the Grantee, the Company or any of
          their Subsidiaries) shall, subsequent to the date of this Agreement,
          acquire beneficial ownership (as such term is defined in Rule 13d-3
          under the Exchange Act) or the right to acquire beneficial ownership
          of, or any Group shall have been formed that beneficially owns, or has
          the right to acquire beneficial ownership (as such term is defined in
          Rule 13d-3 under the Exchange Act) of, (A) 35% or more of the then
          outstanding Company Common Stock and the Plan has failed to receive
          the requisite vote at the Company Shareholders' Meeting or (B) 45% or
          more of the then outstanding Company Common Stock.

          (c) If the Grantee wishes to exercise the Option, it shall send a
     written notice (the date of which being herein referred to as the "Notice
     Date") to the Company specifying (i) the total number of Option Shares it
     intends to purchase pursuant to such exercise and (ii) a place and a date
     not earlier than three Business Days nor later than 15 Business Days from
     the Notice Date for the closing of such purchase (the "Closing Date");
     provided, however, that, if the closing of the purchase and sale pursuant
     to the Option (the "Closing") cannot be consummated by reason of any
     applicable Law, Regulation or Order, the period of time that otherwise
     would run pursuant to this sentence shall run instead from the date on
     which such restriction on consummation has expired or been terminated; and,
     provided, further, that, without limiting the foregoing, if prior
     notification to, or Authorization of, any Governmental Authority is
     required in connection with such purchase, the Grantee and, if applicable,
     the Company shall promptly file the required notice or application for

                            STOCK OPTION AGREEMENT
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     Authorization and shall expeditiously process the same (and the Company
     shall cooperate with the Grantee in the filing of any such notice or
     application and the obtaining of any such Authorization), and the period of
     time that otherwise would run pursuant to this sentence shall run instead
     from the date on which, as the case may be, (i) any required notification
     period has expired or been terminated or (ii) such Authorization has been
     obtained and, in either event, any requisite waiting period has passed.

          (d) Notwithstanding Section 4(c), in no event shall any Closing Date
     be more than 12 after the related Notice Date, and, if the Closing Date
     shall not have occurred within 12 months after the related Notice Date due
     to the failure to obtain any required Authorization of a Governmental
     Authority, the exercise of the Option effected on the Notice Date shall be
     deemed to have expired.  If (i) the Grantee receives official notice that
     an Authorization of any Governmental Authority required for the purchase of
     Option Shares will not be issued or granted or (ii) a Closing Date shall
     not have occurred within 12 months after the related Notice Date due to the
     failure to obtain any such required Authorization of a Governmental
     Authority, the Grantee shall be entitled to exercise its right as set forth
     in Section 7 or to exercise the Option in connection with the resale of the
     Company Common Stock or other securities pursuant to a registration
     statement as provided in Section 9.  The provisions of this Section 4 and
     Section 5 shall apply with appropriate adjustments to any such exercise in
     connection with such a resale.

     5.   Payment and Delivery of Certificates.

          (a) On each Closing Date, the Grantee shall pay to the Company in
     immediately available funds by wire transfer to a bank account designated
     by the Company an amount equal to the Exercise Price multiplied by the
     Option Shares to be purchased on such Closing Date.

          (b) At each Closing, simultaneously with the delivery of immediately
     available funds as provided in Section 5(a), the Company shall deliver to
     the Grantee a certificate or certificates representing the Option Shares to
     be purchased at such Closing, which Option Shares shall be duly authorized,
     validly issued, fully paid and nonassessable and free and clear of all
     Liens, and Grantee shall deliver to the Company its written agreement that
     the Grantee will not offer to sell or otherwise dispose of such Option
     Shares in violation of applicable Law or the provisions of this Agreement.

          (c) Certificates for the Option Shares delivered at each Closing shall
     be endorsed with a restrictive legend that shall read substantially as
     follows:

               THE TRANSFER OF THE STOCK REPRESENTED BY THIS
               CERTIFICATE IS SUBJECT TO RESTRICTIONS ARISING
               UNDER THE SECURITIES ACT OF 1933, AS AMENDED,
               AND PURSUANT TO THE TERMS OF A STOCK OPTION
               AGREEMENT DATED AS OF JUNE 9, 1997. A COPY OF
               SUCH 

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               AGREEMENT WILL BE PROVIDED TO THE HOLDER
               HEREOF WITHOUT CHARGE UPON RECEIPT BY THE
               COMPANY OF A WRITTEN REQUEST THEREFOR.

     A new certificate or certificates evidencing the same number of shares of
     the Company Common Stock will be issued to the Grantee in lieu of the
     certificate bearing the above legend, and such new certificate shall not
     bear such legend, insofar as it applies to the Securities Act, if the
     Grantee shall have delivered to the Company a copy of a letter from the
     staff of the Commission, or an opinion of counsel in form and substance
     reasonably satisfactory to the Company and its counsel, to the effect that
     such legend is not required for purposes of the Securities Act.

     6.   Adjustment Upon Changes in Capitalization, Etc.

          (a) In the event of any change in the Company Common Stock by reason
     of a stock dividend, split-up, combination, recapitalization, exchange of
     shares or similar transaction, the type and number of shares or securities
     subject to the Option, and the Exercise Price therefor, shall be adjusted
     appropriately, and proper provision shall be made in the agreements
     governing such transaction, so that the Grantee shall receive upon exercise
     of the Option the same class and number of outstanding shares or other
     securities or property that Grantee would have received in respect of the
     Company Common Stock if the Option had been exercised immediately prior to
     such event, or the record date therefor, as applicable. If any additional
     shares of Company Common Stock are issued after the date of this Agreement
     (other than pursuant to an event described in the first sentence of this
     Section 6(a)), the number of shares of Company Common Stock then remaining
     subject to the Option shall be adjusted so that, after such issuance of
     additional shares, such number of shares then remaining subject to the
     Option, together with shares theretofore issued pursuant to the Option,
     equals 15.0% of the number of shares of the Company Common Stock then
     issued and outstanding shares of Company Common Stock; provided, however,
     that the number of shares of the Company Common Stock subject to the Option
     shall only be increased to the extent the Company then has available
     authorized but unissued and unreserved shares of the Company Common Stock.

          (b) If the Company shall enter into an agreement (i) to consolidate,
     exchange shares or merge with any Person, other than the Grantee or one of
     its subsidiaries, and,  in the case of a merger, shall not be the
     continuing or surviving corporation, (ii) to permit any Person, other than
     the Grantee or one of its Subsidiaries, to merge into the Company and the
     Company shall be the continuing or surviving corporation, but, in
     connection with such merger, the then outstanding shares of Company Common
     Stock shall be changed into or exchanged for stock or other securities of
     the Company or any other Person or cash or any other property, or the
     shares of Company Common stock outstanding immediately before such merger
     shall after such merger represent less than 50% of the common shares and
     common share equivalents of the Company outstanding immediately after the
     merger or (iii) to sell, lease or otherwise transfer all or substantially
     all of its assets to any Person, other 

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     than the Grantee or one of its Subsidiaries, then, and in each such case,
     the proper provisions shall be made in the agreement governing such
     transaction so that the Option shall, upon the consummation of any such
     transaction and upon the terms and conditions set forth herein, become
     exercisable for the stock, securities, cash or other property that would
     have been received by the Grantee if the Grantee had exercised this Option
     immediately prior to such transaction or the record date for determining
     stockholders entitled to participate therein, as appropriate.

          (c) The provisions of Sections 7, 8, 9, 10 and 11 shall apply with
     appropriate adjustments to any securities for which the Option becomes
     exercisable pursuant to this Section 6.

     7.   Repurchase at the Option of Grantee.

          (a) At any time during the Option Term, at the request of the Grantee
     made at any time after the first Repurchase Event (as hereinafter defined)
     and ending on the first anniversary thereof (the "Put Period"), the Company
     (or any successor thereto) shall repurchase from the Grantee (i) that
     portion of the Option that then remains unexercised and (ii) all (but not
     less than all) the shares of Company Common Stock purchased by the Grantee
     pursuant hereto and with respect to which the Grantee then has beneficial
     ownership. The date on which the Grantee exercises its rights under this
     Section 7 is referred to as the "Grantee Request Date."  Such repurchase
     shall be at an aggregate price (the "Section 7 Repurchase Consideration")
     equal to the sum of:

               (i)   the aggregate exercise price paid (or, in the case of
          Option Shares with respect to which the Option has been exercised but
          the Closing Date has not occurred, payable) by the Grantee for any
          Option Shares as to which the Option has theretofore been exercised
          and with respect to which the Grantee then has beneficial ownership;

               (ii)  the excess, if any, of the Applicable Price (as defined
          below), over the Exercise Price (subject to adjustment pursuant to
          Section 6) paid (or, in the case of Option Shares with respect to
          which the Option has been exercised but the Closing Date has not
          occurred, payable) by the Grantee for each Option Share as to which
          the Option has been exercised and with respect to which the Grantee
          then has beneficial ownership, multiplied by the number of such
          shares; and

               (iii) the excess, if any, of (x) the Applicable Price for each
          share of Company Common Stock over (y) the Exercise Price (subject to
          adjustment pursuant to Section 6), multiplied by the number of Option
          Shares as to which the Option has not been exercised.
 
          (b) If the Grantee exercises its rights under this Section 7, the
     Company shall, within five Business Days after the Grantee Request Date,
     pay the Section 7 Repurchase 

                            STOCK OPTION AGREEMENT
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     Consideration to the Grantee in immediately available funds, and the
     Grantee shall surrender to the Company the Option and the certificates
     evidencing the shares of Company Common Stock purchased thereunder with
     respect to which the Grantee then has beneficial ownership, and the Grantee
     shall warrant to the Company that, immediately prior to the repurchase
     thereof pursuant to this Section 7, the Grantee had sole record and
     beneficial ownership of such shares and that such shares were then held
     free and clear of all Liens.

          (c) For purposes of this Agreement, the "Applicable Price" means the
     highest of (i) the highest purchase price per share paid pursuant a tender
     or exchange offer made for shares of Company Common Stock after the date
     hereof and on or prior to the Grantee Request Date, (ii) the price per
     share to be paid by any third Person for shares of Company Common Stock, in
     each case pursuant to an agreement for a merger or other business
     combination transaction with the Company entered into on or prior to the
     Grantee Request Date, or (iii) the highest bid price per share of Company
     Common Stock as quoted on The Nasdaq National Market (or if Company Common
     Stock is not quoted on The Nasdaq National Market, the highest bid price
     per share as quoted on any other market comprising a part of The Nasdaq
     Stock Market or, if the shares of Company Common Stock are not quoted
     thereon, on the principal trading market (as defined in Regulation M under
     the Exchange Act) on which such shares are traded as reported by a
     recognized source) during the 60 Business Days preceding the Grantee
     Request Date.  If the consideration to be offered, paid or received
     pursuant to either of the foregoing clauses (i) or (ii) shall be other than
     in cash, the value of such consideration shall be determined in good faith
     by an independent nationally recognized investment banking firm selected by
     the Grantee and reasonably acceptable to the Company, which determination
     shall be conclusive for all purposes of this Agreement.

          (d) As used herein, a "Repurchase Event" means the occurrence of any
     Exercise Event.

          (e) Notwithstanding any provision to the contrary in this Agreement,
     the Grantee may not exercise its rights pursuant to this Section 7 in a
     manner that would result in the cash payment to the Grantee of an aggregate
     amount under this Section 7 of more than $12 million, including the amount,
     if any, paid to the Grantee pursuant to Section 9.05(b) of the Plan;
     provided, however, that nothing in this sentence shall limit the Grantee's
     ability to exercise the Option in accordance with its terms.

     8.   Repurchase at the Option of the Company.

          (a) Unless the Grantee shall have previously exercised its rights
     under Section 7, at the request made by the Company at any time during the
     six-month period commencing at the expiration of the Put Period (the "Call
     Period"), the Company may repurchase from the Grantee, and the Grantee
     shall sell to the Company, all (but not less than all) the shares of
     Company Common Stock acquired by the Grantee pursuant hereto and with
     respect to which the Grantee has beneficial ownership at the time of such
     repurchase at a price per 

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     share equal to the greater of (A) the Current Market Price (as hereinafter
     defined) or (B) the Exercise Price per share in respect of the shares so
     acquired (such price per share multiplied by the number of shares of
     Company Common Stock to be repurchased pursuant to this Section 8 being
     herein called the "Section 8 Repurchase Consideration"). The date on which
     the Company exercises its rights under this Section 8 is referred to as the
     "Company Request Date." Notwithstanding the first sentence of this Section
     8(a), the Grantee, within 30 days following the Company Request Date, may
     deliver an Offeror's Notice pursuant to Section 10, in which case the
     provisions of Section 10 and not those of this Section 8 shall control
     (unless the sale to a third Person contemplated thereby is not
     consummated). The Company's rights under this Section 8 shall be suspended
     (and the Call Period shall be extended accordingly) during any period when
     the exercise of such rights would subject the Grantee to liability pursuant
     to Section 16(b) of the Exchange Act by reason of the issuance of the
     Option, any adjustment pursuant to Section 6 hereof, the Grantee's purchase
     of shares of Company Common Stock hereunder or the Grantee's sale of shares
     pursuant to Section 7, 8 or 10.

          (b) If the Company exercises its rights under this Section 8 and the
     Grantee does not deliver an Offeror's Notice or, having delivered an
     Offeror's Notice, the Grantee does not sell the shares to a third Person
     pursuant thereto, the Company shall, within five Business Days after the
     expiration of the Grantee's right to deliver an Offeror's Notice or to sell
     the shares subject to an Offeror's Notice to a third Person, pay the
     Section 8 Repurchase Consideration in immediately available funds, and the
     Grantee shall surrender to the Company certificates evidencing the shares
     of Company Common Stock purchased hereunder, and the Grantee shall warrant
     to the Company that, immediately prior to the repurchase thereof pursuant
     to this Section 8, the Grantee had sole record and beneficial ownership of
     such shares and that such shares were then held free and clear of all
     Liens.

          (c) As used herein, "Current Market Price" means the average closing
     sales price per share of Company Common Stock quoted on The Nasdaq National
     Market (or if Company Common Stock is not quoted on The Nasdaq National
     Market, on any other market comprising a part of The Nasdaq Stock Market
     or, if the shares of Company Common Stock are not quoted thereon, on the
     principal trading market (as defined in Regulation M under the Exchange
     Act) on which such shares are traded as reported by a recognized source)
     for the ten Business Days preceding the date of the Company's request for
     repurchase pursuant to this Section 8.

     9.   Registration Rights.

          (a) The Company shall, if requested by the Grantee at any time and
     from time to time within two years of the first exercise of the Option (the
     "Registration Period"), as expeditiously as practicable, prepare, file and
     cause to be made effective up to two registration statements under the
     Securities Act if such registration is necessary or desirable in order to
     permit the offering, sale and delivery of any or all shares of Company
     Common Stock or other securities that have been acquired by or are issuable
     to the Grantee upon 

                            STOCK OPTION AGREEMENT
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     exercise of the Option in accordance with the intended method of sale or
     other disposition stated by the Grantee, including, at the sole discretion
     of the Company, a "shelf" registration statement under Rule 415 under the
     Securities Act or any successor provision, and the Company shall use all
     reasonable efforts to qualify such shares or other securities under any
     applicable state securities laws. Without the Grantee's prior written
     consent, no other securities may be included in any such registration. The
     Company shall use all reasonable efforts to cause each such registration
     statement to become effective, to obtain all consents or waivers of other
     parties that are required therefor and to keep such registration statement
     effective for such period not in excess of 180 days from the day such
     registration statement first becomes effective as may be reasonably
     necessary to effect such sale or other disposition. The obligations of the
     Company hereunder to file a registration statement and to maintain its
     effectiveness may be suspended for one or more periods of time not
     exceeding 60 days in the aggregate if the Board of Directors of the Company
     shall have determined in good faith that the filing of such registration or
     the maintenance of its effectiveness would require disclosure of nonpublic
     information that would materially and adversely affect the Company. For
     purposes of determining whether two requests have been made under this
     Section 9, only requests relating to a registration statement that has
     become effective under the Securities Act and pursuant to which the Grantee
     has disposed of all shares covered thereby in the manner contemplated
     therein shall be counted.

          (b) The expenses associated with the preparation and filing of any
     such registration statement pursuant to this Section 9 and any sale covered
     thereby (including any fees related to blue sky qualifications and filing
     fees in respect of the National Association of Securities Dealers, Inc.)
     ("Registration Expenses") shall be for the account of the Company except
     for underwriting discounts or commissions or brokers' fees in respect to
     shares to be sold by the Grantee and the fees and disbursements of the
     Grantee's counsel; provided, however, that the Company shall not be
     required to pay for any Registration Expenses with respect to such
     registration if the registration request is subsequently withdrawn at the
     request of the Grantee unless the Grantee agrees to forfeit its right to
     request one registration; and provided further that, if at the time of such
     withdrawal the Grantee has learned of a material adverse change in the
     results of operations, condition (financial or other), business or
     prospects of the Company from that known to the Grantee at the time of its
     request and has withdrawn the request with reasonable promptness following
     disclosure by the Company of such material adverse change, then the Grantee
     shall not be required to pay any of such expenses and shall retain all
     remaining rights to request registration.

          (c)  The Grantee shall provide all information reasonably requested by
     the Company for inclusion in any registration statement to be filed
     hereunder.  If during the Registration Period the Company shall propose to
     register under the Securities Act the offering, sale and delivery of
     Company Common Stock for cash for its own account or for any other
     stockholder of the Company pursuant to a firm underwriting, it shall, in
     addition to the Company's other obligations under this Section 9, allow the
     Grantee the right to 

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     participate in such registration provided that the Grantee participates in
     the underwriting; provided, however, that, if the managing underwriter of
     such offering advises the Company in writing that in its opinion the number
     of shares of Company Common Stock requested to be included in such
     registration exceeds the number that can be sold in such offering, the
     Company shall, after fully including therein all securities to be sold by
     the Company, include the shares requested to be included therein by Grantee
     pro rata (based on the number of shares intended to be included therein)
     with the shares intended to be included therein by Persons other than the
     Company. In connection with any offering, sale and delivery of Company
     Common Stock pursuant to a registration statement effected pursuant to this
     Section 9, the Company and the Grantee shall provide each other and each
     underwriter of the offering with customary representations, warranties and
     covenants, including covenants of indemnification and contribution.

     10.  First Refusal.  At any time after the first occurrence of an Exercise
Event and prior to the second anniversary of the first purchase of shares of
Company Common Stock pursuant to the Option, if the Grantee shall desire to
sell, assign, transfer or otherwise dispose of all or any of the Option Shares
or other securities acquired by it pursuant to the Option, it shall give the
Company written notice of the proposed transaction (an "Offeror's Notice"),
identifying the proposed transferee, accompanied by a copy of a binding offer to
purchase such shares or other securities signed by such transferee and setting
forth the terms of the proposed transaction.  An Offeror's Notice shall be
deemed an offer by the Grantee to the Company, which may be accepted, in whole
but not in part, within ten Business Days of the receipt of such Offeror's
Notice, on the same terms and conditions and at the same price at which the
Grantee is proposing to transfer such shares or other securities to such
transferee.  The purchase of any such shares or other securities by the Company
shall be settled within ten Business Days of the date of the acceptance of the
offer and the purchase price shall be paid to the Grantee in immediately
available funds.  If the Company shall fail or refuse to purchase all the shares
or other securities covered by an Offeror's Notice, the Grantee may, within
sixty days from the date of the Offeror's Notice, sell all, but not less than
all, of such shares or other securities to the proposed transferee at no less
than the price specified and on terms no more favorable than those set forth in
the Offeror's Notice; provided, however, that the provisions of this sentence
shall not limit the rights the Grantee may otherwise have if the Company has
accepted the offer contained in the Offeror's Notice and wrongfully refuses to
purchase the shares or other securities subject thereto.  The requirements of
this Section 10 shall not apply to (a) any disposition as a result of which the
proposed transferee would own beneficially not more than 2% of the outstanding
voting power of the Company, (b) any disposition of Company Common Stock or
other securities by a Person to whom the Grantee has assigned its rights under
the Option with the consent of the Company, (c) any sale by means of a public
offering registered under the Securities Act or (d) any transfer to a wholly
owned Subsidiary of the Grantee which agrees in writing to be bound by the terms
hereof.

     11.  Listing.  If the Company Common Stock or any other securities then
subject to the Option are then listed on The Nasdaq National Market (or if
Company Common Stock is not quoted on The Nasdaq National Market, on any other
market comprising a part of The Nasdaq Stock Market or, if the shares of Company
Common Stock are not quoted thereon, on another trading market or 

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exchange), the Company, upon the occurrence of an Exercise Event, shall promptly
file an application to list on The Nasdaq National Market, such other market
comprising a part of The Nasdaq Stock Market or such other trading market or
exchange, as applicable, the shares of the Company Common Stock or other
securities then subject to the Option and will use all reasonable efforts to
cause such listing application to be approved as promptly as practicable.

     12.  Replacement of Agreement.  Upon receipt by the Company of evidence
reasonably satisfactory to it of the loss, theft, destruction or mutilation of
this Agreement, and (in the case of loss, theft or destruction) of reasonably
satisfactory indemnification, and upon surrender and cancellation of this
Agreement, if mutilated, the Company will execute and deliver a new Agreement of
like tenor and date.  Any such new Agreement shall constitute an additional
contractual obligation of the Company, whether or not the Agreement so lost,
stolen, destroyed or mutilated shall at any time be enforceable by anyone.

     13.  Miscellaneous.

          (a) Expenses.  Except as otherwise provided in the Plan or in Sections
     7, 8 or 9 hereof, each of the parties hereto shall bear and pay all costs
     and expenses incurred by it or on its behalf in connection with the
     transactions contemplated hereunder, including fees and expenses of its own
     financial consultants, investment bankers, accountants and counsel.

          (b) Waiver and Amendment.  Any provision of this Agreement may be
     waived at any time by the party that is entitled to the benefits of such
     provision.  This Agreement may not be modified, amended, altered or
     supplemented except upon the execution and delivery of a written agreement
     executed by the parties hereto.

          (c) Entire Agreement; No Third Party Beneficiary; Severability.
     Except as otherwise set forth in the Plan, this Agreement (including the
     Plan and the other documents and instruments referred to herein and
     therein) (i) constitutes the entire agreement and supersedes all prior
     agreements and understandings, both written and oral, between the parties
     with respect to the subject matter hereof and (ii) is not intended to
     confer upon any Person other than the parties hereto any rights or remedies
     hereunder.  If any term, provision, covenant or restriction of this
     Agreement is held by a court of competent jurisdiction to be invalid, void
     or unenforceable, the remainder of the terms, provisions, covenants and
     restrictions of this Agreement shall remain in full force and effect and
     shall in no way be affected, impaired or invalidated.

          (d) Governing Law.  This Agreement shall be governed by, and construed
     in accordance with, the Laws of the State of Texas, regardless of the Laws
     that might otherwise govern under applicable principles of conflicts of
     law; provided, however, that any matter involving the internal corporate
     affairs of any party hereto shall be governed by the provisions of the
     PBCL.

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          (e) Descriptive Headings.  The descriptive headings contained herein
     are for convenience or reference only and shall not affect in any way the
     meaning or interpretation of this Agreement.

          (f) Notices.  All notices and other communications hereunder shall be
     in writing and shall be deemed given if delivered personally, telecopied
     (with confirmation) or mailed by registered or certified mail (return
     receipt requested) to the parties at the following addresses (or at such
     other address for a party as shall be specified by like notice):

          If to the Company to:

          NUMAR Corporation
          508 Lapp Road
          Malvern, Pennsylvania 19355
          Attention:    Edward P. Delson
                        Senior Vice President and Chief Financial Officer
          Telecopier No.: (610) 644-8131

               with a copy to:

               Drinker Biddle & Reath LLP
               1000 Westlakes Drive
               Suite 300
               Berwyn, Pennsylvania  19312
               Attention: Walter Mostek, Jr.
               Telecopier No.:  (610) 993-8585

          If to Grantee to:

          Halliburton Company
          3600 Lincoln Plaza
          500 North Akard
          Dallas, Texas 75201-3391
          Attention:    Lester L. Coleman
                        Executive Vice President and General Counsel
          Telecopier No.:  (214) 978-2658

                            STOCK OPTION AGREEMENT
                                     -11-
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                      The Exhibit Index appears on Page 4

 
               with a copy to:

               Vinson & Elkins L.L.P.
               2300 First City Tower
               1001 Fannin Street
               Houston, Texas  77002-6760
               Attention:  William E. Joor III, Esq.
               Telecopier No.:  (713) 615-5282

          (g) Counterparts.  This Agreement and any amendments hereto may be
     executed in two counterparts, each of which shall be considered one and the
     same agreement and shall become effective when both counterparts have been
     signed by each of the parties and delivered to the other party, it being
     understood that both parties need not execute the same counterpart.

          (h) Assignment.  Neither this Agreement nor any of the rights,
     interests or obligations hereunder or under the Option shall be assigned by
     either of the parties hereto (whether by operation of law or otherwise)
     without the prior written consent of the other party, except that the
     Grantee may assign this Agreement to a wholly owned Subsidiary of the
     Grantee; provided, however, that no such assignment shall have the effect
     of releasing the Grantee from its obligations hereunder.  Subject to the
     preceding sentence, this Agreement shall be binding upon, inure to the
     benefit of and be enforceable by the parties and their respective
     successors and assigns.

          (i) Further Assurances.  In the event of any exercise of the Option by
     the Grantee, the Company and the Grantee shall execute and deliver all
     other documents and instruments and take all other action that may be
     reasonably necessary in order to consummate the transactions provided for
     by such exercise.

          (j) Specific Performance.  The parties hereto hereby acknowledge and
     agree that the failure of any party to this Agreement to perform its
     agreements and covenants hereunder will cause irreparable injury to the
     other party to this Agreement for which damages, even if available, will
     not be an adequate remedy.  Accordingly, each of the parties hereto hereby
     consents to the granting of equitable relief (including specific
     performance and injunctive relief) by any court of competent jurisdiction
     to enforce any party's obligations hereunder. The parties further agree to
     waive any requirement for the securing or posting of any bond in connection
     with the obtaining of any such equitable relief and that this provision is
     without prejudice to any other rights that the parties hereto may have for
     any failure to perform this Agreement.

                            STOCK OPTION AGREEMENT
                                     -12-

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     IN WITNESS WHEREOF, the Company and the Grantee have caused this Stock
Option Agreement to be signed by their respective officers thereunto duly
authorized, all as of the day and year first written above.

                                    NUMAR CORPORATION


                                    By: /s/ Dr. Melvin N. Miller
                                       -----------------------------------------
                                  Name:  Dr. Melvin N. Miller
                                  Title: Chairman of the Board of Directors
 

                                    HALLIBURTON COMPANY


                                    By: /s/ Lester L. Coleman
                                       -----------------------------------------
                                  Name:  Lester L. Coleman
                                  Title: Executive Vice President and
                                         General Counsel

                            STOCK OPTION AGREEMENT
                                     -13-

                              Page 92 of 99 pages
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