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                                                                   EXHIBIT 10.27

                                                               EXECUTION VERSION


              AMENDMENT NUMBER FOUR TO AGREEMENT FOR PURCHASE AND
                   ASSIGNMENT OF FOREIGN ACCOUNTS RECEIVABLE



          THIS AMENDMENT NUMBER FOUR TO AGREEMENT FOR PURCHASE AND ASSIGNMENT
OF FOREIGN ACCOUNTS RECEIVABLE (this "Amendment"), dated effective as of March
21, 2002, is entered into by and among Grant Geophysical (Int'l) Inc., a Texas
corporation ("Grant"), the entities listed on the signature pages hereof (such
entities, the "Designated Affiliates"), and Elliot Associates, L.P., a Delaware
limited partnership ("Elliott").

          WHEREAS, Grant and Elliott are parties to that certain Agreement for
Purchase and Assignment of Foreign Accounts Receivable, dated August 3, 2001
(as heretofore amended, supplemented or otherwise modified, the "Agreement");

          WHEREAS, Grant has requested that certain provisions of the Agreement
be amended, so as to provide for:

          (a)  an increase in the maximum amount purchased by Elliott from Grant
               of billed and unbilled foreign accounts receivable by $800,000
               (together with any and all sums of money that may become due and
               owing by Grant by reason of this Amendment, the "Incremental
               Obligations"); and

          (b)  a grant of security interest to Elliott by Grant and the
               Designated Affiliates;

          WHEREAS, subject to the terms and conditions set forth in this
Amendment, Grant and Elliott have agreed to amend the Agreement as set forth
more fully below.

          NOW THEREFORE, in consideration of the foregoing and for other good
and valuable consideration, the receipt and adequacy of which is hereby
acknowledged, the parties hereto agree as follows:

          1.   Amendment of Second Paragraph of Preamble of the Agreement. The
second paragraph of the Preamble of the Agreement is hereby amended to read in
its entirety as follows:

          "WHEREAS, Elliott agrees to purchase from Grant up to a maximum amount
          of Eleven Million Seven Hundred Thousand USD ($11,700,000), at any
          point in time, commencing August 3, 2001 and extending through
          September 30, 2002;".

          2.   Amendment of Section 1. Offer of Accounts in the Agreement.

               (a)  Section 1 of Amendment Number Three dated as March 5, 2002
is hereby amended by substitution of "Eleven Million Seven Hundred Thousand USD
($11,700,000)" for "Ten Million Nine Hundred Thousand USD ($10,900,000)".

               (b)  Section 1 of the Agreement is hereby amended by (i)
substitution of "Grant's branch operations in any country in South America,
including but not limited to Ecuador and Colombia" for "Grant's branch
operations in Ecuador and Columbia" and (ii)

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substitution of "any country in South America, including but not limited to
Ecuador and Colombia" for "the countries of Ecuador and Columbia". Grant hereby
grants and re-affirms its grant of a security interest in all of the specific
Grant foreign accounts sold pursuant to the Agreement as amended by this
Amendment.

                  3. Security Interest. Each of Grant and the Designated
Affiliates hereby grants to Elliott a security interest in all currently
existing and hereafter acquired or arising "Collateral" set forth on the
attached Exhibit A, including but not limited to all specific accounts sold,
pursuant to the Agreement, as well as all books and records pertaining to all of
the foregoing, in order to secure (i) prompt repayment of any and all
Incremental Obligations and (ii) prompt performance by Grant and the Designated
Affiliates of their obligations hereunder. Each of Grant and the Designated
Affiliates hereby authorizes Elliott to file such financing statements under the
applicable UCC and agrees to execute and deliver such other documents, and make
such entries and markings in its books and records and take all such other
actions, as Elliott may request to further evidence, perfect, preserve or
protect the security interest granted to Elliott hereunder. Elliott, at its sole
discretion, shall have all rights and remedies with respect to the lien and
security interest herein granted as are provided herein or in the Agreement, the
UCC and other applicable foreign law, including the right at any time, before or
after any default by Grant of any of its obligations hereunder, to notify
account debtors and obligors on instruments to make payment to Elliott (or its
designee) and to take control of proceeds to which Elliott is entitled, and to
apply proceeds to (in addition to other obligations of Grant to Elliott) the
reasonable attorneys' fees and legal expenses incurred by Elliott in connection
with the disposition of collateral or the exercise of other rights and remedies
by Elliott.

                  4. Survival of Representations and Warranties. All
representations and warranties made herein and in the Agreement, and all
representations, warranties and covenants relating to the Collateral under that
certain Loan and Security Agreement, dated as of May 11, 1999 and as heretofore
amended, supplemented or otherwise modified, by and among Grant Geophysical,
Inc., as borrower, the lenders named therein and Foothill Capital Corporation,
as agent, shall survive the execution and delivery of this Amendment, and no
investigation of Elliott or any closing shall affect the representations and
warranties or the right of Elliott to rely upon them.

                  5. Reference to Agreement. The Agreement, as amended hereby,
and all other Exhibits thereto, whether now or hereafter executed and delivered,
are hereby amended so that any reference to the Agreement shall mean a reference
to the Agreement, as amended by this Amendment.

                  6. Continuing Effect; No Other Amendments or Waivers. Except
as expressly amended pursuant to this Amendment, the Agreement is and shall
continue to be in full force and effect in accordance with its terms, and this
Amendment shall not constitute Elliott's consent or indicate its willingness to
consent any other amendment, modification or waiver of the Agreement.

                  7. Severability. Any provision of this Amendment held by a
court of competent jurisdiction to be invalid or unenforceable shall not impair
or invalidate the remainder


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of this Amendment and the effect thereof shall be confined to the provision so
held to be invalid or unenforceable.

     8. Successors and Assigns. This Amendment is binding upon and shall inure
to the benefit of Elliott, Grant, the Designated Affiliates and their
respective successors and assigns, except Grant and the Designated Affiliates
may not assign or transfer any of their rights or obligations hereunder without
the prior written consent of Elliott.

     9. Counterparts. This Amendment may be executed in one or more
counterparts, each of which when so executed shall be deemed to be an original,
but all of which when taken together shall constitute one and the same
instrument.

     10. Facsimile Transmission of Signature. Any party to this Amendment may
indicate its intention to be bound by its execution and delivery of this
Amendment by its signature to the signature page hereof and the delivery of the
signature page hereof, to the other party or its representatives by facsimile
transmission or telecopy. The delivery of a party's signature on the signature
page by facsimile transmission or telecopy shall have the same force and effect
as if such party signed and delivered this Amendment in person.

     11. Governing Law. This Amendment shall be governed by, and construed and
interpreted in accordance with, the laws of the State of New York.


                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]


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     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed and delivered by their respective duly authorized officers as of the
date first above written.

Address for Notices:               GRANT GEOPHYSICAL (INT'L) INC.
16850 Park Row
Houston, Texas 77084
Fax: (281) 398-9996
                                   By: /s/ RUSSELL DUECK
                                       -----------------------------
                                   Name:  Russell Dueck
                                   Title: CFO


Address for Notices:               GRANT GEOPHYSICAL, INC.
16850 Park Row
Houston, Texas 77084
Fax: (281) 398-9996
                                   By: /s/ RUSSELL DUECK
                                       -----------------------------
                                   Name:  Russell Dueck
                                   Title: CFO


Address for Notices:               GRANT GEOPHYSICAL CORP.
16850 Park Row
Houston, Texas 77084
Fax: (281) 398-9996
                                   By: /s/ RUSSELL DUECK
                                       -----------------------------
                                   Name:  Russell Dueck
                                   Title: CFO


Address for Notices:               ADVANCED SEISMIC TECHNOLOGY, INC.
16850 Park Row
Houston, Texas 77084
Fax: (281) 398-9996
                                   By: /s/ RUSSELL DUECK
                                       -----------------------------
                                   Name:  Russell Dueck
                                   Title: CFO


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Address for Notices:                    GRANT GEOPHYSICAL DO BRASIL LTDA.
16850 Park Row
Houston, Texas 77084
Fax:  (281) 398-9996                    By:    /s/ RUSSELL DUECK
                                            ---------------------------------
                                        Name:  RUSSELL DUECK
                                        Title: CFO


Address for Notices:                    PT GRANT GEOPHYSICAL INDONESIA
16850 Park Row
Houston, Texas 77084
Fax:  (281) 398-9996                    By:    /s/ RUSSELL DUECK
                                            ---------------------------------
                                        Name:  RUSSELL DUECK
                                        Title: CFO


Address for Notices:                    SOLID STATE GEOPHYSICAL, INC.
7309 Flint Road S.E.
Calgary, Alberta T2H 1G3
Fax:  (403) 255-4697                    By:    /s/ RUSSELL DUECK
                                            ---------------------------------
                                        Name:  RUSSELL DUECK
                                        Title: VP & GM
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Address for Notices:                    ELLIOTT ASSOCIATES, L.P.
712 Fifth Avenue, 36th Floor
New York, New York 10019
Fax:  (212) 586-9428                    By:    /s/ PAUL SINGER
                                            ---------------------------------
                                        Name:  PAUL SINGER
                                        Title: General Partner
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                                   EXHIBIT A

     "COLLATERAL" means all of Grant's and the Designated Affilates' rights,
title and interest in and to each of the following:

          (a)  the Accounts,

          (b)  the Books,

          (c)  the Equipment,

          (d)  the General Intangibles including, without limitation, the Data
               Library,

          (e)  the Inventory,

          (f)  the Negotiable Collateral,

          (g)  any money or other assets of Grant or any Designated Affiliate
               that now or hereafter come into the possession, custody or
               control of Elliott, and

          (h)  the proceeds and products, whether tangible or intangible, of any
               of the foregoing, including proceeds of insurance covering any or
               all of the Collateral, and any and all Accounts, Books,
               Equipment, General Intangibles, Inventory, Negotiable Collateral,
               money, deposit accounts, or other tangible or intangible property
               resulting from the sale, exchange, collection, or other
               disposition of any of the foregoing, or any portion thereof or
               interest therein, and the proceeds thereof.

     "ACCOUNTS" means all currently existing and hereafter arising accounts,
contract rights, and all other forms of obligations owing to Grant or any
Designated Affiliate arising out of the sale or lease of goods or the rendition
of services by Grant or any Designated Affiliate, irrespective of whether
earned by performance, and any and all credit insurance, guaranties or security
therefor.

     "BOOKS" means all of Grant's and the Designated Affiliates' books and
records including: ledgers; records indicating, summarizing or evidencing
Grant's and the Designated Affiliates' properties or assets (including the
Collateral) or liabilities; all information relating to Grant's and the
Designated Affiliates' business operations or financial condition; and all
computer programs, disk or tape files, printouts, runs or other
computer-prepared information comprising Grant's and the Designated Affiliates'
books and records.

     "DATA LIBRARY" means the presently owned and hereafter acquired
multi-client seismic data of Grant or any Designated Affiliate, which is
marketed broadly on a non-exclusive basis to persons in the oil and gas
industry.

     "EQUIPMENT" means all of Grant's and the Designated Affiliates' present
and hereafter acquired machinery, machine tools, motors, equipment, furniture,
furnishings, fixtures, tools,


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parts, goods (other that consumer goods, farm products or Inventory), wherever
located, including, (a) any interest of Grant or any Designated Affiliate in
any of the foregoing, and (b) all attachments, accessories, accessions,
replacements, substitutions, additions and improvements to any of the foregoing.

     "GENERAL INTANGIBLES" means all of Grant's and the Designated Affiliates'
present and future general intangibles and other personal property (including
contract rights, rights arising under common law, statutes or regulations,
choses or things in action, goodwill, patents, trade names, trademarks, service
marks, copyrights, blueprints, drawings, purchase orders, customer lists, monies
due or recoverable from pension funds, route lists, rights to payment and other
rights under any royalty or licensing agreements, infringement claims, computer
programs, information contained on computer disks or tapes, literature, reports,
catalogs, deposit accounts, insurance premium rebates, tax refunds and tax
refund claims), other than goods, Accounts and Negotiable Collateral.

     "INVENTORY" means all present and future inventory in which Grant or any of
the Designated Affiliates has any interest, including goods held for sale, lease
or license or to be furnished under a contract of service and all of Grant's and
the Designated Affiliates' present and future raw materials, work in process,
finished goods, and packaging and shipping materials and proprietary seismic
data, wherever located.

     "NEGOTIABLE COLLATERAL" means all of Grant's and any of the Designated
Affiliates' present and future letters of credit, notes, drafts, instruments,
investment property, security entitlements, securities (including the shares of
stock of Grant and the Designated Affiliates (except the shares of stock of
Grant Geophysical, Inc.)), documents, personal property leases (wherein Grant or
any Designated Affiliate is the lessor), chattel paper and the Books relating to
any of the foregoing.



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