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Exhibit 10.66

THIRD AMENDMENT TO NOTE PURCHASE AGREEMENTS

          THIS THIRD AMENDMENT

, dated as of October 15, 2001 (the "Amendment"), to the separate Note Purchase
Agreements, dated as of February 12, 1999, is among Seitel, Inc. (the "Company")
and each of the institutions which is a signatory to this Amendment
(collectively, the "Noteholders").

RECITALS:

          A.          The Company and each of the Noteholders have heretofore
entered into separate Note Purchase Agreements dated as of February 12, 1999
(collectively, as amended and in effect immediately prior to the effectiveness
of this Amendment, the "Existing Note Purchase Agreement"), pursuant to which
the Company issued: (a) $20,000,000 aggregate principal amount of its 7.03%
Series D Senior Notes due February 15, 2004 (the "Series D Notes"), (b)
$75,000,000 aggregate principal amount of its 7.28% Series E Senior Notes due
February 15, 2009 (the "Series E Notes"), and (c) $43,000,000 of its 7.43%
Series F Senior Notes due February 15, 2009 (the "Series F Notes", and together
with the Series D Notes and the Series E Notes, the "Notes").

          B.          Capitalized terms used herein shall have the respective
meanings ascribed thereto in the Existing Note Purchase Agreement unless herein
defined or the context shall otherwise require.

          C.          The Company and the Noteholders now desire to amend the
Existing Note Purchase Agreement in the respects, but only in the respects,
hereinafter set forth.

          D.          All requirements of law have been fully complied with and
all other acts and things necessary to make this Amendment a legal, valid and
binding instrument according to its terms for the purposes herein expressed have
been done or performed.

          NOW THEREFORE, for good and valuable consideration the receipt and
sufficiency of which are hereby acknowledged, the Company and the Noteholders do
hereby agree as follows:

1.          AMENDMENTS.

          1.1.          Amendment to Section 10.6(b)(i).

  Section 10.6(b)(i) of the Existing Note Purchase Agreement is hereby amended
and restated in its entirety as follows:

          "(i)          Notwithstanding the provisions of Section 10.6(a), the
determination of whether a Transfer involves a Substantial Portion of the
property of the Company and the Restricted Subsidiaries, as provided in Section
10.6(a)(iii)(A), shall be made without taking into account the same proportion
of the book value attributable to the property subject to such Transfer as shall
be equal to the proportion of the Net Asset Sale Proceeds Amount (the
"Designated Portion") to be applied to either (x) a prepayment of the Notes
pursuant to Section 8.2 of this Agreement and a prepayment of the Additional
Notes pursuant to Section 8.2 of each of the Additional Note Purchase
Agreements, pro rata based on the then outstanding principal amount of and
required Make-Whole Amount (with respect to the Additional Notes, as defined in
each of the Additional Note Purchase Agreements) due with respect to the
prepayment of each series of the Notes and the Additional Notes (a "Prepayment
Transfer") or (y) the acquisition of assets similar to the assets which were the
subject of such Transfer (a "Reinvested Transfer") within one hundred eighty
(180) days of the consummation of such Transfer, as specified in an Officer's
Certificate delivered to each holder prior to, or contemporaneously with, the
consummation of such Transfer."

          1.2.          Amendment to Schedule B.   

Schedule B to the Existing Note Purchase Agreement is hereby amended to add, in
the proper alphabetical order, the following defined terms:

          "Additional Notes - means the 1995 Notes and the 2001 Notes."

          "Additional Note Purchase Agreements - means the 1995 Note Purchase
Agreement and the 2001 Note Purchase Agreement."

          "1995 Notes - means the Company's 7.17% Series A Senior Notes due
December 30, 2001 in the original aggregate principal amount of $25,000,000,
7.17% Series B Senior Notes due December 30, 2002 in the original aggregate
principal amount of $27,500,000 and 7.48% Series C Senior Notes due December 30,
2002 in the original aggregate principal amount of $22,500,000, all issued
pursuant to the 1995 Note Purchase Agreement."

          "1995 Note Purchase Agreement - means each of the separate Note
Purchase Agreements between the Company and the purchasers of the 1995 Notes,
dated as of December 28, 1995, as amended from time to time."

          "2001 Notes - means the Company's 7.04% Series G Senior Notes due
October 15, 2006 in the original aggregate principal amount of $20,000,000,
7.19% Series H Senior Notes due October 15, 2008 in the original aggregate
principal amount of $50,000,000 and 7.34% Series I Senior Notes due October 15],
2011 in the original aggregate principal amount of $37,000,000, all issued
pursuant to the 2001 Note Purchase Agreement."

          "2001 Note Purchase Agreement - means each of the separate Note
Purchase Agreements between the Company and the purchasers of the 2001 Notes,
dated as of October 15, 2001, as amended form time to time.

          1.3.          Amendment to Exhibit A of First Amendment to Note
Purchase Agreement.  

The definition of "Senior Notes" found in Section 1.01 of Exhibit A to the First
Amendment to Note Purchase Agreement is deleted in its entirety and replaced
with the following:

           "Senior Notes" means, collectively, (i) (a) the Company's 7.17%
Series A Senior Notes due December 30, 2001 in the original aggregate principal
amount of $25,000,000, (b) the Company's 7.17% Series B Senior Notes due
December 30, 2002 in the original aggregate principal amount of $27,500,000, and
(c) the Company's Series C Senior Notes due December 30, 2002 in the original
aggregate principal amount of $22,500,000, in each case, issued pursuant to
separate Note Purchase Agreements, dated as of December 28, 1995, as such notes
and agreements may be amended from time to time, (ii) (a) the Company's 7.03%
Series D Senior Notes due February 15, 2004 in the original aggregate principal
amount of $20,000,000, (b) the Company's 7.28% Series E Senior Notes due
February 15, 2009 in the original aggregate principal amount of $75,000,000, and
(c) the Company's Series F Senior Notes due February 15, 2009 in the original
aggregate principal amount of $43,000,000, in each case, issued pursuant to
separate Note Purchase Agreements, dated as of February 12, 1999, as such notes
and agreements may be amended from time to time and (iii) (a) the Company's
7.04% Series G Senior Notes due October 15, 2006 in the original aggregate
principal amount of $20,000,000, (b) the Company's 7.19% Series H Senior Notes
due October 15, 2008 in the original aggregate principal amount of $50,000,000,
and (c) the Company's Series I Senior Notes due October 15, 2011 in the original
aggregate principal amount of $37,000,000, in each case, issued pursuant to
separate Note Purchase Agreements, dated as of October 15, 2001, as such notes
and agreements may be amended from time to time."

2.           REPRESENTATIONS AND WARRANTIES OF THE COMPANY.

          To induce the Noteholders to execute and deliver this Amendment (which
representations shall survive such execution and delivery), the Company
represents and warrants to the Noteholders that:

          (a)          the Company is a corporation duly organized, validly
existing and in good standing under the laws of the state of Delaware;

          (b)          this Amendment has been duly authorized, executed and
delivered by the Company and this Amendment constitutes a legal, valid and
binding obligation, contract and agreement of the Company enforceable against it
in accordance with its terms, except as enforcement may be limited by
bankruptcy, insolvency, reorganization, moratorium or similar laws or equitable
principles relating to or limiting creditors' rights generally;

          (c)          the Existing Note Purchase Agreement, as amended by this
Amendment, constitutes the legal, valid and binding obligation, contract and
agreement of the Company enforceable against it in accordance with its terms,
except as enforcement may be limited by bankruptcy, insolvency, reorganization,
moratorium or similar laws or equitable principles relating to or limiting
creditors' rights generally;

          (d)          the execution, delivery and performance by the Company of
this Amendment (i) has been duly authorized by all requisite corporate action
and, if required, shareholder action, (ii) does not require the consent or
approval of any governmental or regulatory body or agency, and (iii) will not
(A) violate (1) any provision of law, statute, rule or regulation or its
certificate of incorporation or bylaws, (2) any order of any court or any rule,
regulation or order of any other agency or government binding upon it, or (3)
any provision of any material indenture, agreement or other instrument to which
it is a party or by which its properties or assets are or may be bound, or (B)
result in a breach of or constitute (alone or with due notice or lapse of time
or both) a default under any indenture, agreement or other instrument referred
to in clause (iii)(A)(3) of this paragraph (d); and

          (e)          as of the date hereof and after giving effect to this
Amendment, no Default or Event of Default has occurred which is continuing.

3.          MISCELLANEOUS.

          3.1.          This Amendment shall be construed in connection with and
as part of the Existing Note Purchase Agreement, and except as modified and
expressly amended by this Amendment, all terms, conditions and covenants
contained in the Existing Note Purchase Agreement and the Notes are hereby
ratified and shall be and remain in full force and effect.

          3.2.          This Amendment constitutes a contract between the
Company and the Noteholders for the uses and purposes hereinabove set forth, and
may be executed in any number of counterparts, each executed counterpart
constituting an original, but all together only one agreement.

          3.3.          Whenever any of the parties hereto is referred to, such
reference shall be deemed to include the successors and assigns of such party,
and all the promises and agreements contained in this Amendment by or on behalf
of the Company and the Noteholders shall bind and inure to the benefit of the
respective successors and assigns of such parties, whether so expressed or not.

          3.4.          This Amendment constitutes the final written expression
of all of the terms hereof and is a complete and exclusive statement of those
terms.

          3.5.          This Amendment shall be governed by and construed in
accordance with the internal laws of the State of New York.

          3.6.          This Amendment shall become effective at such time as it
has been executed by the Company and the Required Holders.

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          IN WITNESS WHEREOF, the parties hereto have caused the execution of
this Amendment by duly authorized officers of each as of the date hereof.

SEITEL, INC.

   

By:

/s/ Debra D. Valice

Name:

Debra D. Valice

Title:

Executive Vice President

Accepted and Agreed to:

   

[NOTEHOLDER]

By:

 

Name:

 

Title:

 

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